Just when things were starting to get interesting in the MQ, I got that bug where no matter where you go the "You cannot ___ when there are enemies nearby" message will appear.

I've tried getting arrested, but the guards are too busy searching for my invisible enemies. Even if I attack them, they still ignore me.

I gather that you've been to Miscarcand recently. The king is after you.

Try entering an Oblivion Gate. That will probably force the hidden enemy to appear.