This problem might occur in WSUS servers utilizing the internal DB which has several limits and with the huge number of updates and many groups you can face such issue.
To solve this problem and manually remove this Group you will need to work it from the database and edit couple of tables as follows:
- Make Sure to take a backup from your WSUS server and WSUS DB.
- Use SQL Management Studio to connect to Windows internal database \\.\pipe\MSSQL$Microsoft##SSEE\sql\query
- We will mainly remove the old records from tbtargetgroup and tbflattenedtargetgroup tables
- Run “select * from tbtargetgroup” to get the list of groups.
- Identify the TargetGroupID of one of the groups that you want to delete
- Run delete from tbflattenedtargetgroup where TargetGroupID = ‘<TargetGroupID for the group which is to be removed>’
- Run delete from tbdeployment where targetgroupid = ‘<Previous step ID>’
- Run delete from tbtargetgroup where TargetGroupID = ‘<Previous same ID>’
This should take care of the deletion of these groups. Again its always required to ensure you have full backup from your DB.