Have you gotten an “Error 80154B7” or even an “Error 80070571” which are both related to your Xbox Live profile?  Microsoft is aware of the issue, and they have been hearing about these issues since the release of the new dashboard update.

Microsoft is working on this, and in the meantime you can report the problem to Microsoft customer service and get additional help that way. Microsoft continues to work on finding a resolution, but some of the suggested resolutions we have heard from others don’t seem to work; calling Microsoft might be your best option, as they would like to know what you were doing prior to getting this error.