I have tried exporting keys (from Electrum to Electron Cash) as CSV and JSON but I cannot get either to work (again the 'next' button is greyed out).
You should export the private key from Electrum instead of the files you made

From the address you used to get the BCH above
Electrum ('Wallet -> Private keys -> Export') and recreate the wallet in Electron Cash.
Then go to Electron Cash, import the private key that you recieved above. I think it must works
