I hear what your saying. I would suggest maybe trying to replicate it per browser see if its a browser issue like IE versus when you view with mozilla or Chrome etc.
Here is what I know
1. See if it is browser specific.
2. errors are Apache related (i.e. not caused by PhotoPost which is written in PHP)
3. it might be Rewrite Rules, but these are same for all browsers (no rules are browser specific)