Internal Server Error がでたら.

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

Please contact the server administrator, root@localdomain 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.

こんな感じで, Internal Server Error が出たら,
どこかで無限ループしてます.

while とか for とか使ってたらそこ, 要注意です.