Unable to find column "Event category" in grid "SessionWaitsGrid" (4257729)

Getting the error:

Unable to found column "Event category" in grid "SessionWaitsGrid"

in the Activity => Waiting Events drill down.

Remove the config.xml:
--> Go to View/Options/History
--> Select where you store the History
--> Then select Options
--> Select Repository location
--> What you need to do is select/copy the location of this path.
--> Go to windows explore and paste it in there.
--> Once you have done that you will need to go one level up.
--> Once you are there you can delete the config.xml. Remember to shut down Spotlight before you delete the xml.

PLEASE NOTE :
IF YOU DELETE THE WRONG XML SPOTLIGHT WILL NOT WORK. So be careful and do exactly as directed above.