402 payment required error

Hello,
I Installed JA Simpli Quickstart. The front end is working perfectly but I cannot access the backend. As soon as I type the Username and Password, the following error will appear:

Payment Required
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator at webmaster@smartprojectonline.com to inform them of the time this error occurred, and the actions you performed just before this error.
More information about this error may be available in the server error log.
Additionally, a 402 Payment Required error was encountered while trying to use an ErrorDocument to handle the request.

Please check it at :
http://smartprojectonline.com/new/administrator/index.php

Innocent,
Port Harcourt.
Nigeria.
softkamga@yahoo.fr