Run Visual Studio (instance #1) and load your solution
Run a 2nd instance of Visual studio (#2)
From instance #2 go, Debug->Attach to process->Select devenv.exe (instance #1, make sure to select Managed debugging)
Then select Debug->Exception, press "Find.." and search for System.ArgumentNull then check "Thrown"
Go to instance #1, load your view in the designer, this should trigger a break point in instance #2 and it should show you a full stack trace. This information should be enough to identify the offending control/component..