As I had that issue twice already and forgot the solution, I write it down here now 🙂
The issue is, that a search operation in Filenet Admin Console (ACCE) hangs if your browser language is set to a non-english language. Just set English as the default browser language and everything works again.
In SystemOut.log you see a message like that:
This issue is already documented in that technote:
http://www-01.ibm.com/support/docview.wss?uid=swg21662794
“Plugin resource not found” error occurs when using Administration Console for Content Platform Engine (ACCE)