KB Article: http://support.microsoft.com/kb/2579729
Assume that you apply IPsec policies on a computer that is running Windows 7 or Windows Server 2008 R2 and that is located behind hardware load balancing (HLB) equipment in a network environment. In this situation, you may be unable to access a website that is hosted on the computer until the timer for the security association (SA) expires.
Note HLB equipment behaves like a proxy server for client traffic to the computer. Therefore, the computer may believe all traffic is coming from the same source address.