Trouble Network Activating Plugins

Hi All - I'm having trouble network activating plugins on my multisite.

I was able to do this just a day ago, but all of a sudden, I can't do this simple and basic operation.

I am able to go into each subsite and activate plugins - but not Network Activate.

Huh? Any thoughts?

This one's pretty urgent - we're trying to launch a really big site tomorrow.