Please do the following:
1. Clear only the SQLNet datasource history for that connection. This should appear in the list as: “MYDB (SQLNet datasource)” - where "MYDB" is the name of the connection for the affected database.
To delete the history for the “MYDB (SQLNet datasource)”, select the appropriate repository from the “Spotlight Options | Storage | Clear history” screen, and click Delete.
2. Try to connect again.
3. If it still fails, please open a case with Quest support, zip up the contents of the history folder and send that to us as an attachment to the case.
Your root history folder is:
C:\Documents and Settings\<username>\Application Data\Quest Software\Spotlight\Default\History\
… and there should be a sub-folder here, with the name as it appeared in the list of repositories. It should be sufficient to only archive the MYDB repositories. (that is, only the affected connection's repositories)