debug assertion failed

in my code the last line seems to be causing this error. why is this? CBitmap bitmap;
bitmap.LoadBitmap(IDC_STATIC);
//BITMAP bm;
CSize cS = bitmap.GetBitmapDimension();
[184 byte] By [dave2k] at [2007-11-19 19:44:25]
# 1 Re: debug assertion failed
Youy use invalid bitmap ID
DragForce at 2007-11-10 23:43:00 >
# 2 Re: debug assertion failed
doh!

cheers..
dave2k at 2007-11-10 23:44:06 >