I installed the Invite and Admin Message plugins from the WPMU dashboard. And now things are broken in my dashboard. I deleted the plugin folders, but that has not fixed the problem . I have an error message that references problems with lines 3309 and 3312 in my functions.php file. I also can't access several options in the dashboard.
FYI, the plugins description in the WPMU dashboard does not warn that it's only for multisite installation.