Hi Derek,
Have you tried whatever page is issuing the FileDisplay() with different browsers or browsers in safe mode / no addons?
Also, if you have any type of third party security suites installed on either side of the equation, make sure they aren't blocking.
If I were troubleshooting this personally I would break out Wireshark and watch the traffic between the two endpoints. If you aren't familiar with wireshark, you can also do similar stuff in most browsers through the developer tools -> network tab. However, if it is security suite related you probably won't see it make it back to the browser, which is why wireshark on both sides helps.
Cheers!
Ken