History repeats itself. Install this hotfix if you run AV on SBS 2011
Slow Network Performance on SBS 2011
I can't believe we are having a re-run of two years ago, but if you have deployed SBS 2011, you need to run this hotfix if you are running antivirus software on your Small Business Server. Go to http://support.microsoft.com/kb/2493361/ to get it. For some reason unknown to me, the Windows Server Team felt that something released in Server 2008 SP2 wasn't important to put back into Server 2008 R2. I'm glad I have low blood pressure normally, because it just raised a few notches when I found this out.