raster reprojection question

[Deb Sikora]

Hello, 

I've recently downloaded and installed MapServer, and I am trying to use the 
WMS to serve raster images stored as .png w/ .pgw.  The image is displayed 
fine if I use the same projection in the request that I specified in the .map 
file.  If, however, I specify a different projection in the request, I just get a 
solid gray rectangle.

I am new to MapServer, so I apologize if this is an ignorant question, but could 
someone possibly let me know what I might be doing wrong?

Thank you very much,
Deb