We have a tag named error-message, with now 220 questions tagged.

This is quite the meta tag, because it doesn't mean anything and adds no value to a question. Most problems result in some kind of error message, and if you get an error message with a certain program, just tag the question with that program.

Shall we get rid of it?

If anyone wants to do some manual cleanup, just go through the tags in reverse order, and remove it from the questions. Watch out for other bad tags, and fix the post as well if there's anything to fix (e.g. bad titles, "Thanks", and the usual). If you see anything that should be closed and/or deleted, flag away. Please perform edits in smaller batches of 10–20 questions. Doing more will flood the front page unnecessarily.

A manual cleanup—at least a partial one—would be useful to spot bad content, which I'm sure is a little correlated with the use of bad tags.