Symptoms

When trying to cache credentials against a security label in workspace, we saw the following error message. (We were also unable to access the K2 Designer.)
"Error validating credentialcache table. Please contact customer care."
 

Diagnoses

We can only assume that someone played around in the table, this broke something and as a result, things got "locked-up". As a side effect, you are not allowed to open the K2 Designer and you can not cache credentials against a security label. We send the client a "reset validation key", but when we tried to apply it in workspace, we saw the following error: Reference not set to an instance of an object.
 

Resolution

Resolution...
We can only assume that someone made some edits directly to the "CredentialCache" table to get around some other issue.

Fiddling with this table presumably caused the "lock-out" and was the cause for the error when caching credentials against a security label. We then contacted customer care and was provided a "reset validation key", but saw an "object reference" error when trying to apply it. After giving the K2WebService account modify permissions on the "... Host Serverin" directory, we were able to apply the key without any issues.

Additional Information...
Never make direct changes in the K2 DB unless instructed by so by K2 staff. Changing entries in the K2 DB is in direct violation of your support agreement and can potentially void your support agreement.