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?
Ok, a couple of pointers for you in order to know why is it impossible to make cold storage Multisig electrum wallet.
First, a transactions from a multisig wallet requires signatures from
three different private keys, from your wallet and (
two?) from "
Trusted Coin" services which provides the 2FA security.
It will require your client to connect to the server in order for TrustedCoin to sign the transaction.
Second, when you created the Watch only wallet using your cold-storage's xpub key (
master prublic key), it only created a new wallet based on one of the private keys of your wallet, thus, the addresses would be in the
legacy format. (
confirm this by showing the address tab)
Lastly, if the watch-only wallet is funded and you want to spend it, you can make an Air-Gap Cold Storage or a spendable Electrum wallet using the paired xprv key (
master private key) of the xpub key that you have used to make the watch-only wallet.