I've had this happen with different PCs while attempting to download to a 568. Within XP change the 'bits per second' down to half of what it is now. Try a download, and if it still doesn't work try half again. This has solved the problem for me on two different PCs. Of three PCs, one would work at default settings, the other two had to be slowed down. The maximum speed possible seems to be dependent on the PC.