This error message is set by the agent when the agent tries to obtain the post data and encounters an error. To obtain the post, agent tries to get the apache filter configuration and returns the error message "Invalid WebFilter Apache module configuration data" when apache server returns an error to the web agent.
The valid encoding types for POST request are "application/x-www.form-urlencoded", "application/octet-stream" and "text/xml". Per the HTTP specification for "FORM Submission", "application/x-www-urlencoded" is the default encoding type for POST requests.
Any other encoding type (Content-Type header) will be rejected by the Web Agent.