This could be either permissions issue under /var/lib/cloudera-service-monitor or corrupted LevelDB data.
Workaround, if you don't intend to scroll back to past service events, and would like to start SMON you can re-initilaise SMON LevelDB location.
1. Stop Service Monitor
2. [bash]$ mv /var/lib/cloudera-service-monitor /var/lib/cloudera-service-monitor.moved
3. Start SMON, this will initialise your Service Monitor LevelDB/ts data
Awaiting your feedback if this helps.