Steam just released patch 1.4 for Fallout: New Vegas. The current release of vaultmp does not work with this version; I'm going to make it compatible again, might take a few days though.

https://forums.bethsoft.com/index.php...a/page__st__20

(note: as vaultmp relies on NVSE, we will also have to wait until the NVSE team released a compatible version of its script extender - EDIT - already happened, well they are fast)