VCR won't accept all tapes.

@joonastaahl

Are the tapes that don't work all the same brand name?

You could try placing a piece of tape over the record tab (where it has been broken off) but I don't think that this would affect playing a tape, only recording to it.

Check if you can manually wind the tapes which don't work, forward i.e. use a pencil etc to wind forward from the large spool and also to take up the tape onto the smaller spool in the cassette. Sometimes with older tapes that haven't been played for a long time, the tape sticks to itself and doesn't budge. Be careful, not to break the tape when doing this.

Here's the service manual which may help if you have to open the vcr to see if there anything obviously different happening inside when inserting a tape that works and one that doesn't.