Remove device in Manage Devices

I am trying to remove an old computer from my managed devices list. Every time I login to the modem, go to the page and click the X by the name, I get this error:

{"error":"warn","message":"401 Unauthorized!","data":""}

Can you please help? This is really annoying!

This is in the list where I have only allowed devices to access the internet. 

I have already unplugged the modem for 10 seconds, cleared cookies and cache, and tried after that. Need help.