diff --git a/Borepin/Borepin/PageModel/AddServerProcess/AuthPlainPageModel.cs b/Borepin/Borepin/PageModel/AddServerProcess/AuthPlainPageModel.cs
index 4a323b9..81612c4 100644
--- a/Borepin/Borepin/PageModel/AddServerProcess/AuthPlainPageModel.cs
+++ b/Borepin/Borepin/PageModel/AddServerProcess/AuthPlainPageModel.cs
@@ -79,6 +79,12 @@ namespace Borepin.PageModel.AddServerProcess
         public async Task AuthenticateCommandExecute()
         {
             IsBusy = true;
+            if(Username == null || Username == String.Empty || Password == null || Password == String.Empty)
+            {
+                IsBusy = false;
+                return;
+            }
+
             Username = Username.Trim();
 
             _ConnectionData = new ConnectionData()
@@ -116,6 +122,16 @@ namespace Borepin.PageModel.AddServerProcess
                 });
                 return;
             }
+            catch (InvalidCredentialsException)
+            {
+                Device.BeginInvokeOnMainThread(async () =>
+                {
+                    await _PageDialogService.DisplayAlertAsync(Resources.Text.TextResource.ALERT_ConnectionFailed, Resources.Text.TextResource.ALERT_CredentialsInvalid, Resources.Text.TextResource.OK).ConfigureAwait(false);
+
+                    IsBusy = false;
+                });
+                return;
+            }
             catch (AuthenticationFailedException)
             {
                 Device.BeginInvokeOnMainThread(async () =>
@@ -126,7 +142,7 @@ namespace Borepin.PageModel.AddServerProcess
                 });
                 return;
             }
-            catch(Exception)
+            catch(Exception ex)
             {
                 Device.BeginInvokeOnMainThread(async () =>
                 {
diff --git a/Borepin/Borepin/PageModel/ScanURNPageModel.cs b/Borepin/Borepin/PageModel/ScanURNPageModel.cs
index 7974fa4..e047c23 100644
--- a/Borepin/Borepin/PageModel/ScanURNPageModel.cs
+++ b/Borepin/Borepin/PageModel/ScanURNPageModel.cs
@@ -109,7 +109,7 @@ namespace Borepin.PageModel
             {
                 Device.BeginInvokeOnMainThread(async () =>
                 {
-                    await _PageDialogService.DisplayAlertAsync(Resources.Text.TextResource.ALERT, Resources.Text.TextResource.Alert_QRInvalid, Resources.Text.TextResource.OK).ConfigureAwait(false);
+                    await _PageDialogService.DisplayAlertAsync(Resources.Text.TextResource.ALERT, Resources.Text.TextResource.ALERT_QRInvalid, Resources.Text.TextResource.OK).ConfigureAwait(false);
                     IsScanning = true;
                 });
                 return;
diff --git a/Borepin/Borepin/PageModel/StartPageModel.cs b/Borepin/Borepin/PageModel/StartPageModel.cs
index 646d0f4..4c7bfef 100644
--- a/Borepin/Borepin/PageModel/StartPageModel.cs
+++ b/Borepin/Borepin/PageModel/StartPageModel.cs
@@ -69,23 +69,37 @@ namespace Borepin.PageModel
                         }
                     });
                 }
-                catch(Exception ex)
+                catch (ConnectingFailedException)
                 {
-                    if (ex is AuthenticationFailedException)
+                    Device.BeginInvokeOnMainThread(async () =>
                     {
-                        Device.BeginInvokeOnMainThread(async () =>
-                        {
-                            await _PageDialogService.DisplayAlertAsync(Resources.Text.TextResource.ALERT_ConnectionFailed, Resources.Text.TextResource.ALERT_AuthServer, Resources.Text.TextResource.OK).ConfigureAwait(false);
-                        });
-                    }
-                    else if (ex is ConnectingFailedException)
+                        await _PageDialogService.DisplayAlertAsync(Resources.Text.TextResource.ALERT_ConnectionFailed, Resources.Text.TextResource.ALERT_UnableServer, Resources.Text.TextResource.OK).ConfigureAwait(false);
+                    });
+                }
+                catch (AuthenticationFailedException)
+                {
+                    Device.BeginInvokeOnMainThread(async () =>
                     {
-                        Device.BeginInvokeOnMainThread(async () =>
-                        {
-                            await _PageDialogService.DisplayAlertAsync(Resources.Text.TextResource.ALERT_ConnectionFailed, Resources.Text.TextResource.ALERT_UnableServer, Resources.Text.TextResource.OK).ConfigureAwait(false);
-                        });
-                    }
+                        await _PageDialogService.DisplayAlertAsync(Resources.Text.TextResource.ALERT_ConnectionFailed, Resources.Text.TextResource.ALERT_AuthServer, Resources.Text.TextResource.OK).ConfigureAwait(false);
+                    });
+                }
+                catch (InvalidCredentialsException)
+                {
+                    Device.BeginInvokeOnMainThread(async () =>
+                    {
+                        await _PageDialogService.DisplayAlertAsync(Resources.Text.TextResource.ALERT_ConnectionFailed, Resources.Text.TextResource.ALERT_CredentialsInvalid, Resources.Text.TextResource.OK).ConfigureAwait(false);
+                    });
+                }
+                catch (Exception)
+                {
+                    Device.BeginInvokeOnMainThread(async () =>
+                    {
+                        await _PageDialogService.DisplayAlertAsync(Resources.Text.TextResource.ALERT_UnexpectedError, Resources.Text.TextResource.ALERT_UnableServer, Resources.Text.TextResource.OK).ConfigureAwait(false);
+                    });
+                }
 
+                if (_API.IsConnected == false)
+                {
                     Device.BeginInvokeOnMainThread(async () =>
                     {
                         INavigationResult result = await _NavigationService.NavigateAsync("/MainPage/NavigationPage/ServerListPage").ConfigureAwait(false);
diff --git a/Borepin/Borepin/Resources/Text/TextResource.Designer.cs b/Borepin/Borepin/Resources/Text/TextResource.Designer.cs
index 1dc0baf..3b7573e 100644
--- a/Borepin/Borepin/Resources/Text/TextResource.Designer.cs
+++ b/Borepin/Borepin/Resources/Text/TextResource.Designer.cs
@@ -188,6 +188,15 @@ namespace Borepin.Resources.Text {
             }
         }
         
+        /// <summary>
+        ///   Sucht eine lokalisierte Zeichenfolge, die Credentials are invalid. ähnelt.
+        /// </summary>
+        internal static string ALERT_CredentialsInvalid {
+            get {
+                return ResourceManager.GetString("ALERT_CredentialsInvalid", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Sucht eine lokalisierte Zeichenfolge, die Connection already exist. Please delete old Connection before adding the new Connection. ähnelt.
         /// </summary>
@@ -209,9 +218,9 @@ namespace Borepin.Resources.Text {
         /// <summary>
         ///   Sucht eine lokalisierte Zeichenfolge, die QR Code is invalid ähnelt.
         /// </summary>
-        internal static string Alert_QRInvalid {
+        internal static string ALERT_QRInvalid {
             get {
-                return ResourceManager.GetString("Alert_QRInvalid", resourceCulture);
+                return ResourceManager.GetString("ALERT_QRInvalid", resourceCulture);
             }
         }
         
@@ -450,6 +459,15 @@ namespace Borepin.Resources.Text {
             }
         }
         
+        /// <summary>
+        ///   Sucht eine lokalisierte Zeichenfolge, die Unlock ähnelt.
+        /// </summary>
+        internal static string MachinePage_Unlock {
+            get {
+                return ResourceManager.GetString("MachinePage_Unlock", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Sucht eine lokalisierte Zeichenfolge, die Use ähnelt.
         /// </summary>
diff --git a/Borepin/Borepin/Resources/Text/TextResource.resx b/Borepin/Borepin/Resources/Text/TextResource.resx
index fd73670..faa73d3 100644
--- a/Borepin/Borepin/Resources/Text/TextResource.resx
+++ b/Borepin/Borepin/Resources/Text/TextResource.resx
@@ -161,13 +161,16 @@ You can also put down several servers and then connect to the desired server.</v
   <data name="ALERT_ConnectionFailed" xml:space="preserve">
     <value>Connection failed</value>
   </data>
+  <data name="ALERT_CredentialsInvalid" xml:space="preserve">
+    <value>Credentials are invalid.</value>
+  </data>
   <data name="ALERT_DuplicateConnection" xml:space="preserve">
     <value>Connection already exist. Please delete old Connection before adding the new Connection.</value>
   </data>
   <data name="ALERT_PasswordInvalid" xml:space="preserve">
     <value>Password is invalid.</value>
   </data>
-  <data name="Alert_QRInvalid" xml:space="preserve">
+  <data name="ALERT_QRInvalid" xml:space="preserve">
     <value>QR Code is invalid</value>
   </data>
   <data name="ALERT_UnableServer" xml:space="preserve">
@@ -249,6 +252,9 @@ Ask in your Space if you can be trained on the machine to be unlocked for the ma
   <data name="MachinePage_OpenWiki" xml:space="preserve">
     <value>Open Wiki</value>
   </data>
+  <data name="MachinePage_Unlock" xml:space="preserve">
+    <value>Unlock</value>
+  </data>
   <data name="MachinePage_Use" xml:space="preserve">
     <value>Use</value>
   </data>