updateStateOnServer() caught exception notice

Indigo has been running great for many months. Recently, I started receiving the following error:

updateStateOnServer() caught exception: LowLevelBadParameterError -- device value type for state key sensorValue must be real

I haven't added any new devices, plugins, etc. in many weeks. I have no idea how to figure out what is causing this alert. It appears in the Event Log every 22 to 58 seconds.

I discovered an old Oregon Scientific temperature/barometer/humidity device had 'lost its way.' I reset it and all appears to be fine again.