Here's and interesting problem that I encountered this week. I installed Windows Server Update Service (WSUS) a couple of weeks ago on my server. I put the computers into groups and approved all of the updated. I figured I was good to go, but after a week I noticed that I wasn't getting updates at the desktops. Further investigation showed that after I approved the updates the download of the updates failed. After a bit of troubleshooting I determined that the cause was the Gateway Anti-Virus (GAV) and Anti-Spyware (AS) on my SonicWALL TZ170. If I turned the GAV and AS off the updates would download. The troubling part was that the SonicWALL was not logging the failure. I opened a case with SonicWALL and level 1 & 2 support had me try all kinds of things; none of which worked. I finally got to 3rd level support and they had do the following.
Go to http://yoursonicwallip/diag.html Then click on internal settings and check the box for Enable HTTP Byte-Range requests with Gateway AV and apply the change.
This corrected the issue, but I still am waiting on an answer as to why the failure was not being logged. To make things it even more complicated it only seems to be a problem on the Standard OS. I have a client with a TZ170 running the Enhanced OS and WSUS. They have no problems getting the updates to download.
Such is life.