How to fix a ‘User information is disabled’ error on the Canon imageRUNNER Remote UI

This was a pretty weird one, and Google didn’t turn up anything useful, so hopefully this will help anyone with the same problem in future.

Issue

When logging into the Remote UI of a Canon imageRUNNER in System Manager Mode, I got the following message right after entering the System Manager ID and Password, and could not proceed any further:

The problem affected 3 out of 10 of my new printers. All the new printers had replaced existing printers, and I had reused their IP addresses and hostnames. I soon realised that the 3 affected had replaced the 3 Kyocera Mita printers I had, and that all the unaffected printers had replaced different makes.

When I logged in using a different browser, the problem did not occur, so I realised it was something specific to my normal Firefox profile.

Solution

I discovered that the web interface of the previous Kyocera Mita printers had set a cookie named rtl which was the cause of the problem. Removing this cookie for each of the affected printers immediately resolved the problem.