I am having issues where ISA appears to be hanging up where it does not accept any more requests for Active Sync (or OWA which uses the same box). We have had this problem with both a virtualized enviroment (4GB RAM, etc..) as well as a Physical Box. The only way to remediate it is to restart the Windows Firewall Serivce. The physical box seems to work better but additional load causes this issue to occur (2GB). We're running the FW in single NIC mode and we have about 3 issues per day at various times. There are about 30 iPhones who proxy through this ISA server for ActiveSync and less than 10 concurent users using OWA. Both servers are running ISA 2006 sp2 and Windows 2003 sp2.