This happens when you bought or found and old Electrum wallet with balance showing as available. What happens is that such Electrum json file was saved with information regarding a known blockchain transaction that is real and can be seen in Blockchain but as stupid as Electrum is they do not match address to public key and only read the json file and then you see a transaction as valid and even allows you to create a transaction but you can not send it because Electrum does not have the keys to sign the transaction. It does not matter if you have a seed. Such seed does not generate your address with balance and it is only there because it was read from a forged json file. So, this error appears. You do not have the real seed.