This method/property must be called on the UI thread. Fix the problem by testing the InvokeRequired property on the control and call Invoke() or BeginInvoke() on the control instead of calling directly when InvokeRequired is true. InvokeRequiredException, Sdl.DesktopEditor.Control, Version=15.2.0.1041, Culture=neutral, PublicKeyToken=c28cdb26c445c888 Sdl.DesktopEditor.Control -2146233088 SDL Trados Studio 15.0.0.0 15.2.0.1041 Microsoft Windows 10 Home NULL 1033 1252 DESKTOP\User 4.0.30319.42000 DESKTOP True 8278156 MB