We were having some problems getting Windows Server Update Services (WSUS) to download new updates at one of our customer's sites.  The ISA server was denying the connections, but was saying that "an existing connection was forcibly closed by the remote host".  I made several changes on the ISA server to try to fix this.  I tried using an HTTP rule without the web proxy, disabled caching, etc.  Nothing seemed to fix the problem.  When I checked the Application event log on the server, there was a WSUS error saying, "Content file download failed. Reason: The server does not support the necessary HTTP protocol. Background Intelligent Transfer Service (BITS) requires that the server support the Range protocol header."  I did some research on this and found a fix that involved making a change to the WSUS database. [more]

I stopped the WSUS service and ran the following command:
osql.exe -S PNB-TS\MICROSOFT##SSEE -E -b -n -Q "USE SUSDB update tbConfigurationC set BitsDownloadPriorityForeground=1"

I then restarted the service and it worked great.