We contacted Microsoft to find out if there was a common cause that we could report on and help prevent. We've only heard about these problems since the new Xbox Live dashboard became available earlier this month.
"We have recently identified an Xbox Live profile data error that results in Error Code '801540B7' for a small number of Xbox Live members. The error instructs users to attempt to re-download their Xbox Live profile and directs them to customer service support for further assistance," a Microsoft spokesperson told Joystiq. "We apologize for the inconvenience this has caused to our loyal Xbox Live members and are working to resolve the issue as soon as possible."
If you've experienced error "801540B7," or a similar profile error, contact us and describe exactly what happened when the error occurred.