This is an old thread, but here is how a client of mine, who got the same External Exception message yesterday, resolved it...
I found out what was causing the issues we were troubleshooting and have resolved it. It was, in fact, a network issue. Since the machine was virtualized, it was making network calls faster then windows server 2008 allowed. As such, the server was flagging the communications as a denial-of-service attack and shutting down the channel. There were a couple of registry settings that needed to be adjusted. I have restarted the server and checked the applications. It seems to be better.