Only text menu available

I'm trying to get v1.4.0001 working on an overclocked pi B.

It boots directly to the text menu (no sign of the GUI) after the spash screen.

When I select "3" (Start Amiga) from the menu, the following message flashes before the screen refreshes:

/usr/local/bin/amiga: line 4: [some number] illegal instruction ./6 -f conf/autostart.uae

where [some number] starts around 400 after boot, and increases with each attempt.

I tried editing /usr/local/bin/amiga to use a different conf file, but got the same error.

Any ideas? Should I try 1.313.xxxx

Thanks!