Sounds like a flaky web server issue, though I may be missing some important detail. Is this by any chance some sort of AJAX implementation, or just a straight-ahead PHP page being called directly by the browser? (I'm not sure why that would matter, mind you.)
"Please give us a simple answer, so that we don't have to think, because if we think, we might find answers that don't fit the way we want the world to be."
~ Terry Pratchett in Nation