screen problems

1
hi - I see this has come up before, but I can't find a satisfactory
answer:

running the demos (as well as other script) in the latest
(post-august 5) version of Psychtoolbox (matlab R12, windows 2000,
pentium 4), I constantly get the following error...

DLL load failed for mex file
C:\matlabR12\toolbox\psychtoolbox\psychbasic\Screen.dll
The specified module could not be found.

??? Invalid MEX-file

Error in ==> C:\matlabR12\toolbox\psychtoolbox\psychdemos\GratingDemo.m
On line 15 ==> window=SCREEN(whichScreen,'OpenWindow');


does anyone know what the problem might be?
thanks very much
chris summerfield