Any Help ?
From what I know this error usually means the Alerting engine is having problem connecting to the SQL Server. Since they are both on the same machine it may be a problem with SQL server not responding to the transaction from alerting engine quickly enough. You might want to open a ticket on this one as there could be multiple reasons why this could happen: Resource issue on the server, could be a environmental problem... Some things I would ask myself: did this just start happening or is it progressively getting worse as the database grows, is the server its self healthy resource wise. How often are the log messages showing up (all the time or just once in a while) and what version are you running?
When you say...
My Solarwinds NPM and SQL DB on the same system.
do you mean they are on the same server? If this is the case, then that try moving your SQL DB to another server as a test. You can find SQL Server requirements on page 11 of the Orion NPM Administrator Guide and general NPM requirements on page 10.