Error 500 al instalar Virtuemart

[kaneko82]

Buenas:

Estoy intentando instalar Virtuemart 2.0 sobre Joomla 1.6 y me sale un mensaje de error 500 y no hay forma de continuar. Igualmente me sale el error instaladon cualquier otro módulo o plugin, pero si recargas la web, acaba haciendose el proceso correctamente.

El error del Virtuemart es este:

Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, no-reply@x10hosting.com and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

Muchas gracias por adelantado.