PhotoPaint X5 Invalid File Name Error on Processing X3 and X4 Images

Hello, I have used photopaint X3 and X4 to process some images but now when I am trying to open them in photopaint X5, they won't open.
I get the following error on my screen:

Corel PHOTO-PAINT
Invalid file name.
OK
I am having no problems when I am using X3 and X4 on the same files. Any help will be highly appreciated.
Kindest regards
