While opening nworks UI, you see the following error:
"Object reference not set to an instance of an object"
The maindb.xml file is corrupted for some reason.
It is necessary to remove the "maindb.xml" file in the following way:
Locate and backup file "C:\Documents and Settings\All Users\Application Data\nworks\Management Center\maindb.xml" (for Win 2008 the location is "C:\ProgramData\nworks\Management Center”)
Stop nworks Enterprise Manager (Management Center) service
Delete file "C:\Documents and Settings\All Users\Application Data\nworks\Management Center\maindb.xml" (for Win 2008 the location is "C:\ProgramData\nworks\Management Center”)
Start nworks Enterprise Manager (Management Center) service
Once the service is started again, "maindb.xml" will be recreated.
NOTE: Removing maindb.xml file removes all the vCenter connection configuration, each VEM server advanced property customization, and VEM server ESX cluster assignments.