Ok please tell me what i am doing wrong:
1. I already transfered my BTC to Bittrex so I dont need to create another electrum wallet for transfer.
2. I downloaded Electron Cash
3. Try to setup wallet from existing seed - Cannot press 'Next' button when trying to create.
Don't you still have your Bitcoin wallet file from when you transfered your BTC to Bittrex? You can just open the same file in Electron Cash instead of creating the same wallet again (in Electron Cash) with your seed. Both wallet files are compatible with each other, so you can open a Electrum wallet in Electron Cash and vice versa.
I'm not sure what is the issue there. You should be missing a word from the seed or something like this.
You can:
a. Do like I said above and open your BTC wallet in Electron Cash
Or
b. Open your Electrum (BTC) wallet again and check if the seed you are trying to input is correct by checking if it's the same found in Wallet -> Seed.