What display do you use and is its firmware the latest?

Post your flarmcfg.txt file here - it may explain the problem (or email it to me).

You haven't answered what firmware for your CORE you're running.

You haven't answered what size USB drive you're using, nor confirmed it's USB 2.0, nor what it is formatted as.

Have you tried downloading with someone else's USB drive, which is confirmed to work?