The most recent version of Helix firmware that we recommend for non-encoded Helixes is version 2.56 b2. Note that the 2.55 b9 firmware version has been pre-loaded on several Helixes. There is a bug in the 2.55 b9 GUI, so we recommend using the 2.56 b2 GUI (available here), even if you are using the 2.55 b9 firmware.
If you have already upgraded the firmware on your non-encoded Helix, then you may be best off downgrading to 2.56 b2, because we have default profiles available for that version. If you downgrade, you will have to load default profiles, THEN calibrate again.
For encoded Helixes, we recommend using the version your Helix was shipped with for the time being.