Please try the following:
Go to Start | Programs | Quest Software | Performance Analysis | Performance Analysis.
Select under connections, StealthCollect for SQL Server. Double click on New Connection.
In the New Properties dialog, click Add/Remove Instances and then click on the refresh
button. Close the Add/Remove Instances. Cancel the New Properties dialog.
Highlight the SQL Server instance you were trying to connect to in Performance Analysis
Profiles dialog and hit connect.
If you still see the same issue after doing the above, then please raise a case with support.