Shoutbox

That string can be found a lot in Core.js.

To add the fix suggested by aasselin you need to edit Core.js.

Find each line which contains:
    GetDWordValue(HKEY_CURRENT_USER, MPLkey, 'AllowMultiClients')
and change it to:
    GetDWordValue(HKEY_CURRENT_USER, MPLkey + '\\GlobalSettings', 'AllowMultiClients')
You should find 9 of such lines.

Do not change the line
    var MPLkey = 'SOFTWARE\\Patchou\\Messenger Plus! Live';
since the variable MPLKey will also be used in some other script files.

Note that this fix is not supported, nor properly tested by the original author of the script and you may not redistribute the modified version without the approval of the original author of this script.