Internal Server Error with a mod

[SoloDZ]

hello just installed this ajax chat mod: http://custom.simplemachines.org/mods/index.php?mod=1319
everytime i get this error:
Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator, [email protected] 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.

Please tell me what is the problem
please reply as soon as possible
thank you:)

[SoloDZ]

EDIT: solved just had to CHMOD chat/index.php and shoutBox/index.php to 755
thanks to the mod FAQ