I Just tried to adjust some PID values on my Runner using MultiWii, but I couldn’t read or write the data. Which was strange, since it used to work that way several times before. Beside reading or writing the data everything went fine, drivers are installed and the Runner was initially responding on his assigned COM Port.
This issue is related to the FTDI driver. According to this comment Walkera uses a counterfeit FTDI chip for serial to USB connection. Downgrading to an older driver version does the trick. On my Win 7 x64 Machine I went from 2.12.10 back to 2.10.00 and flashing the firmware, reading or writing data works like a charm.