Ctrl+F4 is not a script, it's a built-in command that custom scripts can overwrite. If you want it to work again, you would have to delete the alias cF4 from the script you are using.
To attempt to delete it, type
/alias cF4. If you get an error saying "does not exist" it's probably defined in a remote file. In this case you can type
//echo -a $isalias(cF4).fname to find out where it's hiding, then open your remote (ALT+R), locate it and delete it.
Alternatively, use
Alt+Z. You might even find it easier to press