M60 Errors

I have 2 Premieres, one purchased in 2010, the other last year. During the last month, each of them has spontaneously lost all Guide data usually accompanied by a M60 Error message [All Show Data has run out. Connect to TiVo service - blah, blah, blah]. This has happened more than once on each box. When this happens, all program data in the Guide shows "To Be Announced". However, Channel Banners do show name of show in progress, and name of next show. Shows continue to be recorded. In every case, the TiVo Status shows that a successful connection had been made to the TiVo service within the last 24 hours. In fact, forcing a connection does not cure the problem. The only cure is to restart the TiVo. After restart the Guide data re-appears for next 14 days. In one case, I'd actually perused the Guide an hour before this error had occurred, for a program a week in the future, and all the Guide data was there. An hour later the TiVo popped up this error message, and all the Guide data had disappeared.

If this had happened on just one box, I would have thought it was a problem particular to that box. But since it has happened multiple times on both, it has to be something else. Any suggestions?