init.php

[mudmin]

So the error 500 makes me think that you have error reporting turned off on your server so you're not getting a proper idea of what's wrong.
Add this starting at line 2 of your init.php

Code:

error_reporting(E_ALL);

Code:

ini_set('display_errors', 1);

In theory, that should give you a more specific error to see if your code is wrong. If your code seems right, try adding your concat thing to

Code:

usersc/includes/head_tags.php

That will get it into the header but after init has done its thing.