Not sure what the error could be, you might have used the wrong public key, or you are using a "Non-deterministic watch-only wallet" when you should use a "Deterministic watch-only wallet", as you stated that you're using electrum.
Are you sure you're using your MPK ( Master Public Key) when trying to create a watch-only adress?
https://bitcoinelectrum.com/creating-a-watch-only-wallet/You solved my problem after all AdolfinWolf. You we're kinda right.
I was using the right MPK, but I didn't notice I had 3 cosigners and I needed to import all 3 MPK for all 3 cosigners.
Problem solved, thanks again.