Actionscript 3 :: URLRequest Or Loader Simply Not Working On Some Computers?

So my problem may be a little bigger than that, but I'm not certain. I'm creating a custom flash photo viewer for a client that dynamically loads the images with Loader objects. It takes a folder name in a specified directory on the server and calls a php page (using URLRequest) to get the workable contents of the folder. And then it loads it up from that array.

Here's the problem: it works FINE on my machine and every machine I've tested it on, but it DOESN'T work on my client's machine or some of his customer's machines. The loader bar that's at the bottom of the screen doesn't start to fill, which means that the images aren't starting to even load, and the status bar indicates that it continues to wait for a the server, yet never finishes waiting. This is consistent on a single machine, but varies across machines.

I've added diagnostics (a custom class I made to track certain vars and collect errors) to the thing to catch any errors, but it reports nothing on my client's machine. I've added flash version checking code, so the possibility of a lower version messing it up is gone... I guess my question is, is there anything (security, environment, etc) that I could have overlooked that doesn't allow request objects or something to work on certain machines?? I've been ripping my hair out trying to figure this out!

[Code]....