It is definite that the al_create_bitmap call to the Allegro 5 library wasn't able to return the desired VRAM bitmap. Allegro 5 calls OpenGL or DirectX behind the scenes and thereby allocates VRAM for us. Allegro 5 doesn't know about savestates, it merely knows about bitmaps. If this call fails, my code throws an exception.
Until 0.9.1, this exception flew out of the program unhandled, terminating the program and displaying the error message. On 0.9.2 and newer, I catch this exception during savestate construction, do not savestate instead, and continue the program.
-- Simon