sermaton

yes, you need to see php error log. It can be not enough permissions or just server admin not providen MODIFY permission for your mysql user.

looks like it was some php syntax error in code (or in wordpress template).

You need to modify it in templates or in plugin code.

I think no php-mbstring installed on server. Please check it.

I think you must to use password, it not will work in other way.

winrar also can extract your tar.gz archive.

winrar also can extract your tar.gr archive.