cannot save projects with more than 1 bitmap image

I’m working on a standalone PC with WinXP PRO SP2.
Installed is TBSE V2.0.3
When I try to save a project which has more than 1 bitmap image, I get the following error message:
Error while saving the animation set
Unable to save the image file Image-1.tga.new
Unable to save the image file Image-2.tga.new
Unable to access file image-1.tga.new

With projects with just 1 bitmap I don’t have a problem.

Any suggestions?
Is this a restriction of TBS Express?