So it turns out it's some network error. It can be cleared by entering the following sequence on your Zesa meter:
1)zero then your meter number
3)your meter number again immediately followed by
4)your new token number
Was also advised that if you generally keep your meter plugged into the mains it's advisable to remove the back up batteries. Not sure if there's any link to the error code but steps 1-5 above worked for me.