A Windows Based Computer that is connected to your network via an IP Phone (NAP-Enabled) may not connect to the same VLAN after resume from hibernation

This issue applies to Windows XP – SP3, Windows Vista – SP2, Windows Server 2008 – SP2, Windows Server 2008 R2 – SP1 and Windows 7 – SP1.

This issue occurs on networks that use IEEE 802.1X authentication where the client computer or server machine is connected or bridged via a NAP-Enabled device such as an IP or VoIP Phone Handset.

The issue will not be resolved for Windows XP because it is now outside the mainstream support cycle.  Hotfixes for the other operating systems listed above can be obtain via Microsoft KB 976373 http://support.microsoft.com/kb/976373