Edit, I am using multisig when I received the error.
I created a test single signature wallet, and offline signing worked just fine....hmmm.
Any advice how to do multisig in an offline, cold storage environment?
Is there any chance that the "error" is being generated by the "co-signer pool" plugin?

ie. it is trying to send the "partially signed" transaction to the pool for signing by co-signers, but obviously fails because it is an offline, airgapped machine.
Is that plugin enabled by default on all MultiSig wallets? or does the user have to explicitly enable it?
