I had a problem where my 522 could not detect a dial tone from time to time and I would get the nag screen.
running the phone connection check also showed the problem and a reboot would correct things.
broadband phone users have reported issues with the nightly check in the past.
The 522 checks for a dial tone during the nightly update check.
If your phone line is in use at that time you will also get the Nag screen.
You can change the daily update check time if its currently set to a time your phone line is in use.
If none of the above apply you may have a hardware issue with the 522.
The bottom line seems to be as long as the Box can make its monthly call-in to uplaod any PPV purchases you won't get charged the $5 mirror fee.