Problems with Authentication

We have turned on Microsoft authentication on the folder containing php pages for a web application I have been developing and we are getting weird things happening now. I can pull up a page the first time, but if it ends in php, the second and future times of pulling the page up gives me the following CGI Error:

The specified CGI application misbehaved by not returning a complete set of HTTP headers. The headers it did return are:

Has anyone run into this problem before or know the fix for it??