Some USB sticks are partitioned so that manufacturer-supplied software can always run and this can possibly interfere with what the update process is expecting. Sandisk Cruzer is a case in point. I had a stick (Sandisk Cruzer) where it didn't work, a different stick (Kingston Datatraveler) was fine with exactly the same procedure. Apart from that, formatting as FAT32 is required, and the .bin file the only single thing on the stick.
(You can get rid of the Sandisk partition, but it is easier to use a different make)