Invalid bitmap with wxWidget 2.6.1

[pbpb]

Hello,
I have an exception in my wxWidgets program (ver 2.6.1 on Windows 7,
compiler Borland C++ builder 5) on function wxDC::Blit
Assert says :
"bmp.Ok() && bmp.HasAlpha()" failed: AlphaBlt(): invalid bitmap
I have saved my image with multiple GUI : Paint.NET, PSP5,
PhotoFiltre ...
Sometimes, it works, another time, it does'nt work. I don't understand
why.
At loading time, I create a mask if the image has no mask :
mask = bitmap->GetMask();
if (!mask) {
mask = new wxMask(*bitmap, *wxWHITE);
bitmap->SetMask(mask);
}
It works everytime if the image has no mask -> SetMask
It never works when the image has already a mask.
I join with this message an image which is working good, and another
which is not working.
Thank you for your response.
Pierre

[Preben Friis]

bitmap->UseAlpha(); // ... ?

/Preben Friis