ISA Server stopped responding, so I had to make a trip back into town to see what was going on. Firewall service had crashed, so I rebooted. Found the following three errors in the Application Event Log: The Firewall service stopped because an application filter module C:\Program Files\Microsoft ISA Server\ISAMON2.dll generated an exception code C0000005 in address 251F1A7A when function CompleteAsyncIO was called. To resolve this error, remove recently installed application filters and restart the service. Faulting application wspsrv.exe, version 4.0.2163.213, stamp 420bdbd0, faulting module isamon2.dll, version 2.0.0.2, stamp 40b1fcdf, debug? 0, fault address 0x00001a7a. Due to an unexpected error, the service fwsrv stopped responding to all requests. Stop the service or the corresponding process if it does not respond, and then start it again. Check the Windows event Viewer for related error messages. I only have SurfControl and GFI WebFilter in as application filters installed outside of ISA's. Any idea what might have caused this?