WORKAROUND: Add the desired error message to look for in the Error Log Entries w/ scanning checked. Then use the Error Log Count alarm. The problems with workaround are: 1. the alarm is a count alarm so the specific error message will not be included in the email; 2. If monitoring for more than one specific error, those will get grouped (remember this is a count alarm) and only one email will get sent; 3. Count alarm will only fire off notification if the count changes.
STATUS: Enhancement request number SoSSE-2551 has been submitted to Development for consideration in a future release of Spotlight on SQL Server Enterprise.