This seems like an old topic, but since no responses are recent, I am wondering if there is new server behavior to be aware of.
We use a perl script (formmail) to send info from a user filled out form back to us. This process has been in place for at least 7 years (based on file properties) and had been working perfectly. Until last week. Now, this error is generated:
The specified CGI application misbehaved by not returning a complete set of HTTP headers.
Nothing has been changed on our site (by us). I have looked at the paths on the script and they do correspond with our site's path, and permissions are all set correctly.
I did initiate a support ticket, but they seem unable to make useful suggestions, claiming that "Technical Specialists are not developers", so am reaching out to the list for other suggestions.