Lots of Xbox 360 and Xbox One users are currently unable to log in to Xbox Live. Attempting to log into the service is causing many users to see an error with the code an error with the code 0x87DD000F. Microsoft is aware of this issue, and they’ve updated the Xbox support page to state that they are hard at work on fixing the problem. Hopefully all those affected will be able to return to their normal gaming activities soon!
Source: Xbox Support