OK, third time's a charm, wiped & re-installed again - everything seems to be working fine now. Thanks for your offer of help, yokos, much appreciated - but I think I'm ok now. (I have noticed this with other homebrew applications, though - a need to install them 2 or 3 times before they would work properly. A strange and inexplicable reluctance on the Iliad's part to accept non-Irex software?)
I did notice that I do get the empty question mark file if I hit Update while something is playing, so maybe that was the problem. Stopping play and updating again solved it.
Still no working gnuchess or emelFM2, though, no idea why, reinstalled them several times now. They both seem to have an identical hiccup - they start loading, green LED flashes wildly for a second, progress indicator starts up, then a screen refresh back to square one.
They both stopped working after the first Jukebox installation, but I can't tell for sure if it was the cause.
Ah, the joys of inofficial community software beta-testing ...
