Add WebException handlers to prevent them reaching the UI.

src/NzbDrone.Core/Download/Clients/Deluge/DelugeProxy.cs

@@ -229,6 +229,10 @@ namespace NzbDrone.Core.Download.Clients.Deluge
                     throw new DownloadClientException("Unable to connect to Deluge, please check your settings", ex);
                 }
             }
+            catch (WebException ex)
+            {
+                throw new DownloadClientException("Unable to connect to Deluge, please check your settings", ex);
+            }
         }
 
         private void AuthenticateClient(JsonRpcRequestBuilder requestBuilder, DelugeSettings settings, bool reauthenticate = false)

src/NzbDrone.Core/Download/Clients/NzbVortex/NzbVortexProxy.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Net;
 using Newtonsoft.Json;
 using NLog;
 using NzbDrone.Common.Cache;
@@ -158,6 +159,10 @@ namespace NzbDrone.Core.Download.Clients.NzbVortex
             {
                 throw new DownloadClientException("Unable to connect to NZBVortex, please check your settings", ex);
             }
+            catch (WebException ex)
+            {
+                throw new DownloadClientException("Unable to connect to NZBVortex, please check your settings", ex);
+            }
         }
 
         private void AuthenticateClient(HttpRequestBuilder requestBuilder, NzbVortexSettings settings, bool reauthenticate = false)

src/NzbDrone.Core/Download/Clients/Nzbget/NzbgetProxy.cs

@@ -174,6 +174,10 @@ namespace NzbDrone.Core.Download.Clients.Nzbget
 
                 throw new DownloadClientException("Unable to connect to NzbGet. " + ex.Message, ex);
             }
+            catch (WebException ex)
+            {
+                throw new DownloadClientException("Unable to connect to NzbGet. " + ex.Message, ex);
+            }
 
             _logger.Trace("Response: {0}", response.Content);
 

src/NzbDrone.Core/Download/Clients/Sabnzbd/SabnzbdProxy.cs

@@ -5,6 +5,7 @@ using NzbDrone.Common.Extensions;
 using NzbDrone.Common.Serializer;
 using NzbDrone.Core.Download.Clients.Sabnzbd.Responses;
 using NzbDrone.Common.Http;
+using System.Net;
 
 namespace NzbDrone.Core.Download.Clients.Sabnzbd
 {
@@ -167,6 +168,10 @@ namespace NzbDrone.Core.Download.Clients.Sabnzbd
             {
                 throw new DownloadClientException("Unable to connect to SABnzbd, please check your settings", ex);
             }
+            catch (WebException ex)
+            {
+                throw new DownloadClientException("Unable to connect to SABnzbd, please check your settings", ex);
+            }
 
             _logger.Trace("Response: {0}", response.Content);
 

src/NzbDrone.Core/Download/Clients/qBittorrent/QBittorrentProxy.cs

@@ -160,9 +160,13 @@ namespace NzbDrone.Core.Download.Clients.QBittorrent
                 }
                 else
                 {
-                    throw new DownloadClientException("Failed to connect to download client", ex);
+                    throw new DownloadClientException("Failed to connect to qBitTorrent, check your settings.", ex);
                 }
             }
+            catch (WebException ex)
+            {
+                throw new DownloadClientException("Failed to connect to qBitTorrent, please check your settings.", ex);
+            }
 
             return Json.Deserialize<TResult>(response.Content);
         }
@@ -201,7 +205,11 @@ namespace NzbDrone.Core.Download.Clients.QBittorrent
                         throw new DownloadClientAuthenticationException("Failed to authenticate with qbitTorrent.", ex);
                     }
 
-                    throw;
+                    throw new DownloadClientException("Failed to connect to qBitTorrent, please check your settings.", ex);
+                }
+                catch (WebException ex)
+                {
+                    throw new DownloadClientException("Failed to connect to qBitTorrent, please check your settings.", ex);
                 }
 
                 if (response.Content != "Ok.") // returns "Fails." on bad login

src/NzbDrone.Core/Download/Clients/uTorrent/UTorrentProxy.cs

@@ -193,6 +193,10 @@ namespace NzbDrone.Core.Download.Clients.UTorrent
                     throw new DownloadClientException("Unable to connect to Deluge, please check your settings", ex);
                 }
             }
+            catch (WebException ex)
+            {
+                throw new DownloadClientException("Unable to connect to Deluge, please check your settings", ex);
+            }
 
             return Json.Deserialize<UTorrentResponse>(response.Content);
         }
@@ -230,7 +234,11 @@ namespace NzbDrone.Core.Download.Clients.UTorrent
                         throw new DownloadClientAuthenticationException("Failed to authenticate with uTorrent.");
                     }
 
-                    throw;
+                    throw new DownloadClientException("Unable to connect to uTorrent, please check your settings", ex);
+                }
+                catch (WebException ex)
+                {
+                    throw new DownloadClientException("Unable to connect to uTorrent, please check your settings", ex);
                 }
 
                 cookies = response.GetCookies();