welcome, now you are a true member of nexus.
things like this happen every now and then with the mod manager from nexus.
It's really funny as just a month ago the modding community went crazy about Bethesda. Now nexus saw this and decided "we can top it" by making the mod manager stop working.
Why not having both ways until the new plugin is known to be working. It's out for a few hours with already at least 3 updates. 2 of them not working and the last refusing to install completely.
Give the team around that plugin a bit of time. I'm sure they will get it to work.