Error Value cannot be null. Parameter name:solutionDirectory

If you do not show us your code (the whole segment) and wich line throws the exception, we can only guess.

This sounds like the Function checks the paramters before execution and tells you that one Argument that should not be null, is null (nothing in VB). Hence it throws a ArgumentNull Exception so you can fix that.

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Let's talk about MVVM: http://social.msdn.microsoft.com/Forums/en-US/wpf/thread/b1a8bf14-4acd-4d77-9df8-bdb95b02dbe2 Please mark post as helpfull and answers respectively.