I got one of these exact letters a few years ago. The person I spoke to at the City Hall said it was because my insurance had been revoked (ed. note: It had not. I knew it had not. I confirmed it had not.). They reinstated my permit while we were on the phone because they couldn't find the "paper trail" from the audit they had done. All that to say, it's probably an administrative error and I hope it's sorted as easily for you!