MSN Messenger 7.5 is a beta release meant for official testers. If you are such a tester you should be aware that you need to test MSN Messenger 7.5 without using additional third-party add-ons. If you are not a tester then you should not be using MSN Messenger 7.5.
That said, the latest version of Messenger Plus! was released before MSN Messenger 7.5 was released. Compatibility problems may therefore very well arise; they should be addressed in a newer version