BPOS: Application is unable to connect; if this problem persists, contact your service administrator

Configuring the BPOS Sign in tool the following message appears:

• Application is unable to connect;  if this problem persists, contact your service administrator.
• La aplicación no puede conectarse; si el problema persiste, contacte con su administrador.

The root of the problem is a miss-configuration of the permissions of the certificates store. To solve it try the following command (run it from an admin account):

cacls "%appdata%\Microsoft\Crypto\RSA" /t /e /c /g %userdomain%\%username%:F

Solution originally posted here: http://social.technet.microsoft.com/Forums/en/onlineservicessigninapplication/thread/548c57b4-dc62-4638-9e81-57eabc8af6d2