Plugins not available after multisite upgrade

Hi guys,
I was working on a social network and had the bright idea that everyone should get their own blog late in the game. So I upgraded my installation to multisite, to my dismay a key plugin, the group calendar is no longer coming up on the site. It seems i can activate it as a network admin, but it no longer appears in the plugins list on my original site.

any suggestions on what may be going on?

thanks!