This error is usually the result of an improperly written CGI script that, as the error suggests, is not sending the proper headers. I ran into this error from my own CGI scripts until I added a "Content-type: text/html" header followed by a blank line before returning anything else. This assumes, of course, that what you're returning is actually text/html. You may wish to do some further research on this topic to ensure that your script is correctly written for whatever it is you're trying to do with it.