Complete reboot seens to have worked.
I am using the version of MySensos binding that is included in the latest openhab2 using the apt-get install. I downloaded the latest binding from git, but when I put it into the addons folder openhab gave an exception saying it could not load the SNAPSHOT jar as there was already another binding loaded with a higher version, so I removed it.
I still have a slight problem, whilst the Light-Level sensor is sending data: (BH 1750 reporting lux)
250;3;1;0;37;196 The sensor readout is still showing NaN, however the LastUpdated date/time is being updated