VPN site-to-site connections may not work after enabling NLB.
In an array-based TMG 2010 deployment with Integrated NLB enabled, traffic may not reach its destination. The most visible example is IPSec/PPTP/L2TP VPN site-to-site with NLB enabled, where resources are inaccessible on either side of the tunnel as soon as Integrated NLB is enabled. Please note that this software update is a language-neutral release and may be installed on all languages of Forefront TMG 2010.
KB980674 (not online yet at time of this writing)