I don't use elephant-bird, so I'm not entirely sure that this is the problem.
But looking at their build for v2.2.3, it was compiled against hadoop-0.20.2 and pig-0.9.2. I've seen problems with UDFs in Pig when running on a newer version than what the UDF was compiled against.
Are you able to upgrade elephant-bird to a newer version or recompile against the correct libraries?