i'm having an issue with this and "fastcgi" on Microsoft-IIS/6.0

I can install the entire module, but installation of the functions_bmz_image_handler.php breaks the front end of site giving this error:
----
FastCGI Error

The FastCGI Handler was unable to process the request.
Error Details:

The FastCGI process exited unexpectedly
Error Number: -2147467259 (0x80004005).
Error Description: Unspecified error
HTTP Error 500 - Server Error.
Internet Information Services (IIS)
----

the back end survives, until i try to access the image handler module, and i get the same error.

any suggestions for troubleshooting? i have it working on my 1.3.9h live site (w/ IH3), but cannot get it to work on my 1.5.1 beta (w/ IH4), running on the same server. it also works fine on my local MAMP server i used to set up the 1.5.1.