Error: Certificate limit reached
You are signing into WebMatrix and you get an error that there are not more certificates available. This happens because as part of sign-in, WebMatrix downloads a management certificate in order to retrieve your websites and provision new websites with Windows Azure. There is a limit of 25 certificates available per subscription.
Things you can try
If you signed into another computer, you can sign out to delete the certificate. You can directly delete any unused certificates in the Windows Azure portal, click here to learn how. Before deleting any certificates, be sure they are not being used with another tool or computer.