Problems with save file (serialize)!

Hello all,
My problem is that:
I open a new document and work with it.
then I save it.
then i change it (continue working with it...)
then i want to save it, so i press at the 'save file' but nothing happend!
this operation DOES NOT call the serialize function (of CDocument) as it should be!
why?
thanks,
Lesner.

Did you call the CDocument::SetModifiedFlag function after changing your document?

Yes i called the SetModifiedFlag() !