We have a PIX 525 running 7.2(2). Recently, without any network changes, one particular webserver in the DMZ network became unreachable. Other webservers in that same network can be reached as normal. In doing packet captures both inside and in the dmz, it looks like the page request goes out and the page comes back and gets as far as the dmz interface. In packet captures on the inside network, an ACK is received from the server for the page request, and that's the last thing received on that session. Subsequent attempts seem normal until that point, too.
We have a standby PIX and we've tried doing a failover to that, and that device is showing the same behavior.