Disablement from outlook is usually caused by Outlook not shutting down properly and then picking the likely culprit (usually the last item to unload or be stuck unloading) and then disables that Add-In.

You can try re-enabling it from the Tools -> Trust Center -> Add-Ins (tab) then press the Go button at the bottom and re-check Enterprise Vault Add-In

I've seen this happen usually with the Fast Shutdown enabled for Outlook

does it let you install the client on the server now? if JW's idea doesn't work you could just try installing the client. it used to stop you because of mapi issues or something but i think that may be fixed.

i actually typed don't install the client about 100 times, but thought it may be better to just say, please don't install the client :)

will the sun explode?

well both the client and the server both write to HKLM\Software\KVS\Enterprise Vault
And some people decide to install the client and put it on a different drive and it updates the InstallPath to the location of the client, unfortunately when you restart services it then looks to the new install location and fails in spectacular fashion................

then the sun explodes

the sun definitely explodes!!!!!!!!

maybe we can say that it's not the end of the world as long as you install it to the same location as existing EV?

No, do not install the client on the EV server.  It is not necessary and can cause other issues.