MapServer Application Error

[Stephen King]

Hi,
I've been setting up a test application using MapServer 4.4.1 on a Windows
XP Professional machine with IIS. Everything works fairly well apart from
an occaisional mapserv.exe - Application Error box that appears with a
message such as:

The instruction at "0x7c93426d" referenced memory at "0x00000000". The
memory could not be "read". Click on OK to terminate the program. Click on
CANCEL to debug the program.

My application currently has 7 layers, six of which are vector and one
raster (ECW format). Originally I had more raster layers, and I thought
that this was causing the problem, however, even without them I still have
this problem. Sometimes the error also causes images in the legend not to
be written correctly.

On another, perhaps related note, I have set the application up as a WMS
server. I can access this through ArcGIS 9, however, it will not display
all 7 layers at the same time, rather only six are visible in the map,
even if all seven are switched on.

Would be grateful if anyone can give me an idea what this problem is.

Many thanks,
Stephen