After site migration website looks fine, only the login does not work

I have a strange problem with a website.
We migrated the site from one server to another one.
There were some small problems at first (broken links) which were resolved easily and now the website itself looks fine.

However, when trying to login at wp-admin (or wp-login.php) nothing happens. No error appears, the page simply refreshes and shows the login fields again.

So I activated debug mode in the wp-config.php file, by changing it to: define(‘WP_DEBUG’, true);

and now the following message appears (not sure if this has anything to do with the problem of not being able to log in)

Notice: wp_enqueue_script was called incorrectly. Scripts and styles should not be registered or enqueued until the wp_enqueue_scripts, admin_enqueue_scripts, or login_enqueue_scripts hooks. Please see Debugging in WordPress for more information. (This message was added in version 3.3.) in …/wp-includes/functions.php on line 3547.

I checked the mentioned line in the mentioned file, but I’m not sure what’s wrong, this is the line:

trigger_error( sprintf( __( ‘%1$s was called incorrectly. %2$s %3$s’ ), $function, $message, $version ) );

Any idea what is causing this problem?