Please take a look at the attached sample mission, as it would answer all your questions so far.

As you can see inside the mission.sqm of the attached example mission, there are no mods involved.

If these errors are really only produced by engine code and not by referencing errors related to script variables or commands, then these errors should not be pushed into the RPT, because no one can make any sense of them and they fill up the rpt for no reason like spam.