Spawn, try changing the J code to an indicator with the "albumart" code. I think the way the Mp3art plugin works is that it only wants the indicator to work on one screen. The workaround I used with blue's strings plugin works, but only shows the folder image (no embedded art) but updates with each song.
I think the root issue started after the 10/26/07 release, there's something that doesn't play well with the indicators. I think mitchjs's version doesn't have this issue according to sonic, so maybe try that version and see if it works. There's some discussion on the RRGAS thread about the way plug-ins are handled, starting about the 14th or 15th posts.