diff --git a/Desktop.Win/Services/ShutdownServiceWin.cs b/Desktop.Win/Services/ShutdownServiceWin.cs
index a2bebb39..1b75f46d 100644
--- a/Desktop.Win/Services/ShutdownServiceWin.cs
+++ b/Desktop.Win/Services/ShutdownServiceWin.cs
@@ -6,6 +6,7 @@ using Remotely.Shared.Utilities;
 using System;
 using System.Diagnostics;
 using System.Threading.Tasks;
+using System.Windows;
 
 namespace Remotely.Desktop.Win.Services
 {
@@ -17,12 +18,12 @@ namespace Remotely.Desktop.Win.Services
             var casterSocket = ServiceContainer.Instance.GetRequiredService<CasterSocket>();
             await casterSocket.DisconnectAllViewers();
             await casterSocket.Disconnect();
-            System.Windows.Forms.Application.Exit();
-            App.Current.Dispatcher.Invoke(() =>
+            Application.Current.Dispatcher.Invoke(() =>
             {
-                App.Current.Shutdown();
-
+                Application.Current.Shutdown();
             });
+            System.Windows.Forms.Application.Exit();
+            Environment.Exit(0);
         }
     }
 }
diff --git a/Server/Hubs/ViewerHub.cs b/Server/Hubs/ViewerHub.cs
index 2cc1bb55..3781b0a0 100644
--- a/Server/Hubs/ViewerHub.cs
+++ b/Server/Hubs/ViewerHub.cs
@@ -99,6 +99,11 @@ namespace Remotely.Server.Hubs
 
         public Task SendDtoToClient(byte[] baseDto)
         {
+            if (string.IsNullOrWhiteSpace(ScreenCasterID))
+            {
+                return Task.CompletedTask;
+            }
+
             return CasterHubContext.Clients.Client(ScreenCasterID).SendAsync("SendDtoToClient", baseDto, Context.ConnectionId);
         }
 
@@ -109,7 +114,7 @@ namespace Remotely.Server.Hubs
 
         public override Task OnDisconnectedAsync(Exception exception)
         {
-            if (ScreenCasterID != null)
+            if (!string.IsNullOrWhiteSpace(ScreenCasterID))
             {
                 CasterHubContext.Clients.Client(ScreenCasterID).SendAsync("ViewerDisconnected", Context.ConnectionId);
             }
@@ -129,6 +134,11 @@ namespace Remotely.Server.Hubs
 
         public async Task SendScreenCastRequestToDevice(string screenCasterID, string requesterName, int remoteControlMode, string otp)
         {
+            if (string.IsNullOrWhiteSpace(screenCasterID))
+            {
+                return;
+            }
+
             if ((RemoteControlMode)remoteControlMode == RemoteControlMode.Normal)
             {
                 if (!CasterHub.SessionInfoList.Any(x => x.Value.AttendedSessionID == screenCasterID))
diff --git a/Server/Services/DataService.cs b/Server/Services/DataService.cs
index ad617f10..c3297677 100644
--- a/Server/Services/DataService.cs
+++ b/Server/Services/DataService.cs
@@ -486,11 +486,11 @@ namespace Remotely.Server.Services
 
         public bool DoesUserExist(string userName)
         {
-            if (userName == null)
+            if (string.IsNullOrWhiteSpace(userName))
             {
                 return false;
             }
-            return RemotelyContext.Users.Any(x => x.UserName == userName);
+            return RemotelyContext.Users.Any(x => x.UserName.Trim().ToLower() == userName.Trim().ToLower());
         }
 
         public bool DoesUserHaveAccessToDevice(string deviceID, RemotelyUser remotelyUser)
diff --git a/Shared/ViewModels/Organization/Invite.cs b/Shared/ViewModels/Organization/Invite.cs
index cfe9e0a7..72132d1a 100644
--- a/Shared/ViewModels/Organization/Invite.cs
+++ b/Shared/ViewModels/Organization/Invite.cs
@@ -1,4 +1,5 @@
 using System;
+using System.ComponentModel.DataAnnotations;
 
 namespace Remotely.Shared.ViewModels.Organization
 {
@@ -7,6 +8,7 @@ namespace Remotely.Shared.ViewModels.Organization
         public string ID { get; set; }
         public bool IsAdmin { get; set; }
         public DateTimeOffset DateSent { get; set; }
+        [EmailAddress]
         public string InvitedUser { get; set; }
     }
 }