>Hi,
>
>I have a project that has MainWindow and a couple of forms. The forms are called from the menu of the MainWindow form. After I manually changed namespace of forms things stopped working. Do I have to make sure that all forms of the project must have the same namespace? (or maybe something else caused the problem).

You can have different namespaces with no problem. When you change them manually, just don't forget the partial classes that are generated by the design system. You need to change them there as well. Then of course depending on how you named them, you would have to have the using statements when you reference them from somewhere else.
Tim