I apologize that upgrading firmware on OS 2.1 has been so difficult. This has not been an issue I anticipated at all when designing OS 2.1. The initial firmwares on all OS 2.1 units were flashed through the USB port, using the bootloader, so we know it worked at least upon the time of testing. We’ve also tested the driver on all major operating systems. But I guess computers differ, and we don’t have the resources to perform wider testing (other than using the computers we have). That’s why from OS 2.2 we’ve changed to use a USB-serial chip and optiboot bootloader, which seems to have much less issues. In any case, I am just explaining the background. For any user who can’t upgrade their OS 2.1, we offer upgrade service free of charge.