Thanks for the suggestions. I tried adding the AddHandler line to .htaccess but the error appeared almost immediately.

I had not noticed this error until I started testing the shipping modules. I cloned a few and installed the Staticlist mod. I think the error appeared before I installed the mod but I don't recall.

Over the past few days the error occurred when I was testing the shipping and checkout but today it happened when I tried to log in, so it may not be specific to shopping cart processing.

Unfortunately, we're hosted on GoDaddy and their support is useless.
For example, I asked about creating a custom 500 error page and they told me it wasn't possible. Fortunately I found this page:
http://www.codestyle.org/sitemanager...#apache-config

When I asked for help with this FastCGI error, they said I can either use their own webcart product or buy a dedicated server account. They refuse to admit it could be anything their server is doing and blame Zen Cart coding.

KMF