Apache Server error Port 80

URGENT: I received the following:
It still occurs after changing it back. Some of the sites pages are accessible, some aren’t. I have limited access editing WP Admin mode and get the same error even when restoring to previous saved versions.

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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 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.

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Apache Server at lifepurposegroup.com Port 80