unable to merge object

[HandsFree]

Cat reported a crash in my game: room38 line 5 Error: MergeObject: unable to merge object due to color depth differences.
She used DirectDraw 5 while I tested with Direct 3D 9.

The code for room 38 is:
function room_AfterFadeIn()
{
oTownsquare.MergeIntoBackground();// this is line 5
Wait(40);
...
}

Is there anything I can do to prevent this?
thanks

[monkey0506]

Yes, you can import an object sprite and a room background that are the same color depth.

[HandsFree]

I have no idea what color depth is. That's way I made a RON game, so I could just use existing art.
However, this background is completely black (end credits) so I think I've probably not used a background picture at all.
Does it makes sense that the oTownsquare.MergeIntoBackground (when there is no background) works with Direct 3D 9 but not with DirectDraw 5?