Hi Taf
I just got the same player and am just getting to grips with it.
Apparently it has problems playing DivX avi files as opposed to xvid avi. My theory is that the manufacturer has not licensed DivX. The machine is probably using the Xvid Home Profile. The workaround is to change the 4CC from DV50 or whatever to an appropriate xvid equivalent. you can use Mpeg4Modifier to do this.
http://moitah.net/
Oh the machine will only recognise fat16/32 formatted USB sticks.
HTH