Try to follow these steps:
1. Make sure your server meets ALL the script requirements.
2. Re-upload the original/unmodified files to your server.
3. Disable SQL mode in your server (e.g. remove the ONLY_FULL_GROUP_BY, ERROR_FOR_DIVISION_BY_ZERO, etc in the SQL mode). If you don't know how to do this, you can ask your hosting provider to get assistance. We sure your hosting provider will happy to do this for you.
Regarding messages from users, if the member sending message using the feedback form, admin will get the message through email. Make sure the email settings configured properly.