As for my understanding, at first in flow isValid2 was used but after the upgrade, right me if I am wrong, I think so now isValid2 may be deprecated therefore it is giving a strange error. you can also check this post
http://forum.flow.com/t/is-it-possible-to-do-an-ecrecover-of-an-ethereum-address-in-a-cadence-contract/684
http://forum.flow.com/t/deploying-contracts-and-signing-transaction-from-node/657