VS2005, VA 1525, C++
i added the following line to an existing class in a .h file:
int SomeFunc(long l) { return l * 4; }
then i placed the caret inside SomeFunc and used the VAssistX -> refactoring menu, on the toolbar, and Move Implementation to Source File worked perfectly for me.
what code are you trying this on, and how are you triggering the menu / which menu are you triggering?
are other refactoring operations available to you?