Webform: 500 Error upon submission

When I submit a webform it generates the following message:
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Internal Server Error

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

Please contact the server administrator, webmaster@----------.net and inform them of the time the error occurred, and anything you might have done that may have caused the error.

More information a

Checking the server error log and it seems that the error has something to do with the permission setting. i changed the permission on capture.php to 755 and it seems to work.

however, i checked the permissions on a different installation which does work and the permission setting for capture.php in that installation is 777.

the webforms folder setting is 755 on both installations. by the way, both installations are with the same host but in different accounts. the install that is not working is a copy of the install that is working!

is there a tool to verify that the install is not corrupt?