Throw a better error when we try and fail to load something.

EduNetworkBuilder/TrippleDESDocumentEncryption.cs

@@ -128,10 +128,19 @@ namespace EduNetworkBuilder
             EncryptedXml exml = new EncryptedXml();
 
             // Decrypt the element using the symmetric key.
+            try
+            {
+                //Do the decryption
                 byte[] rgbOutput = exml.DecryptData(ed, algValue);
-
                 // Replace the encryptedData element with the plaintext XML elemnt.
                 exml.ReplaceData(encryptedElement, rgbOutput);
+            }
+            catch
+            {
+                //The decryption failed.
+                throw new LoginException("Key/Salt unable to decrypt.");
+            }
+
 
         }
 
@@ -186,4 +195,19 @@ namespace EduNetworkBuilder
         }
 
     }
+
+    /// <summary>
+    /// Create a simple login exception that we can throw when we try to decrypt and it fails
+    /// </summary>
+    public class LoginException : System.Exception
+    {
+        public LoginException() : base()
+        { }
+
+        public LoginException(String message) : base(message)
+        { }
+
+        public LoginException(String message, Exception innerException) : base(message, innerException)
+        { }
+    }
 }