Accidentally deleted WSUS Computer/Computer Group from WSUSAdmin Console
SCENARIO 1:
Computer group accidentally deleted from WSUSAdmin Console??
RESOLUTION
Don’t panic, this is at least not the DR situation!! All you have to do is to re-create the COMPUTER GROUP in WSUSAdmin console with the same name. Be patient, till WUA completes the next detection cycle & the computers will re-populate again in the newly created group using Client Side Targeting. If you are not using CST, then you have to manually move the computers from "Unassigned Computers" to the newly created group.
SCENARIO 2:
Computer/PC accidentally deleted from the respective Computer group in WSUSAdmin Console??
RESOLUTION
The same logic applies here. It will re-register at the time of next detection cycle.
MORE INFORMATION
WSUS Clients Showing Unknown in Reports Status of Computers
http://msmvps.com/blogs/athif/archive/2005/09/06/65554.aspx
Quick Automatic Update Client Detection & Installation with Windows Server Updates Services:
http://msmvps.com/athif/archive/2005/06/29/56200.aspx
WSUS: Script to Force the Update Detection from Automatic Update Client for updates on WSUS Server:
http://support.microsoft.com/kb/555453