PlgBlt(..) transparency Parameter

When using PlgBlt:

pDC->PlgBlt(currentImagePoints, &memDC, 0, 0, 66, 80, CBitmap(), 0, 0);

I get just an ordinary sprite (contained in the memDC).  But instead, i want to use the transparency mask parameter and replace the above CBitmap()  parameter with my monocrome mask.

The problem however is that it's not displaying the sprite at all whatsoever now.  When i try shrinking the size of the mask bitmap (so that it is smaller than the bitmap contained in memDC), the sprite to be displayed to the screen is still invisible!

The mask that i tried making was done as follows:
- Loaded Photoshop
- Opened the bimap that contains the sprite (red in the transparency area)
- went to mode and selected Grey Scale
- saved the bitmap with the name mask.bmp

The mask is specified to be monocrome in the MSDN library.

Could you give any suggestions as to why the sprite is always invisible no matter what?  What can i do to fix this?

- Thanks