There are issues with IMDB searching from EPG. Sometimes it works and sometimes it does not.

It seems that it fails when there is more than one match, and no way to choose between them. However, the actual problem is not very clear.

http://forum.team-mediaportal.com/mediaportal-1-2-0-beta-540/imdb-lookup-mytv-98559/

http://forum.team-mediaportal.com/bugreports-74/tv-epg-imdb-feature-not-working-105294/