In the next version we will probably add some additional code so that if it can’t bind ipv6 it will go back to ipv4 only. Initially the ipv6 feature was added due to a pull request:
https://github.com/OpenSprinkler/OpenSprinkler-Firmware/pull/49
and those who had trouble with it are generally due to using a very old version of Raspbian that doesn’t support ipv6. The solution is to either upgrade Raspbian or roll back to an earlier version of firmware. Upgrading Raspbian is a better solution since the future firmwares may rely on other features that are not available in older Raspbians.