You can temporarily disable NOD32 for its GUI which will allow you to install Messenger Plus!.
Afterwards you can delete the installer and re-enable NOD32 without being bothered by it again. Which is again showing Messenger Plus! is clean. If it really did install the malware which Eset is claiming it does then it should be able to find traces of it after installation. I see you are already agree it is clean, but if anyone else reading this wants more information or discuss it, see
eset nod32 blocked messenger plus 3.85.