Usually it is caused by condensation, for example when you take the camcorder from an aircon environment into a warm humid place. The moisture in the air condenses inside the cold cam and the internal sensor gives you this warning.
If the tape is damp it will cling to the heads and rollers, and for sure something would get damaged. that's why camcorders have these sensors to prevent operating the cam in such conditions.
If you allow the cam to warm up and dry off it will be OK. If you can put it in sunlight for a few minutes that will help dry it faster (but don't cook it!).