The following link shows the list of software updates and hotfixes for Hyper-V in Windows Server 2008 / Windows Server 2008 R2. . These updates and hotfixes can help avoid some known issues and may save you a support call.
Comprehensive list of Hyper-V R2 updates/Hotfixes
Comprehensive list of Hyper-V updates/Hotfixes
Last Updated: May 26, 2010 / Posting on blog: July 28, 2010