I did have the same error, found it it was either the custom field was deleted or altered, or it wasnt configured the right way, try to delete the custom field and make a new one and see, also empty the cache.
Cheers!
FORGET THE ABOVE!!1 the error came back, also in backend print view it displays this {"429":" Choose a colour : <\/span>62"} VM 2.0 and J1.5.X