Getting error when I activate Global Site Search

I'm getting this error when I network activate Global Site Search:

The plugin generated 1104 characters of unexpected output during activation. If you notice “headers already sent” messages, problems with syndication feeds or other issues, try deactivating or removing this plugin.

This includes stuff like undefined offset on 201 and undefined variable on 278. Not a big deal except the sheer amount and the fact that the search is returning no results.

It may be unrelated but I'm not getting any search results on the /site-search page when I search. I have post indexer installed and working great. I've installed version 2 of this plugin before on another client site with pretty good results.