WIN: Error: Restore failed to restore the Direct Draw Surface

1
Hi there!

I'm encountering a strange error message, and got no idea how to deal
with it.

I'm presenting a number of different stimuli by producing OffScreen
windows and subsequently copy them onto the screen. Subjects have to
make pointing movements with the mouse. Hence the cursor position is
manipulated I introduced a fake cursor, which is implemented with the
Screen(win, 'FillOval',c,coords) instruction:

Screen(Window, 'Waitblanking');
Screen(Window, 'FillOval',black, CursorCoord);


This works fine in a 'for' loop. However, I wanted to nest this loop
into another simple 'for' loop. But then the program stops with the
following error message:

??? Restore failed to restore the Direct Draw Surface

Error in ==> TrainPoint at 140
Screen(Window, 'FillOval',black, CursorCoord);

Has anyone a hint how to fix this?

I'm running Matlab 7.01 on WIn XP with the PTB 2.54

Thanks a lot,
Annette