Hey, I also have the problem trying to import a private key from MultiBit into Electron Cash. The next button is always greyed out even though my key is not password protected.

When I exported the multibit classic key it gave me a .key file. Is that what I need?

Any help for a noob is much appreciated. Thanks!

edit: The key appears to be in this format according to the comments in the file: <Base58 encoded private key>[<whitespace>[<key createdAt>]]

Apparently you can't use this kind of compressed key to import into modern wallets. Any ideas on how to export in a format or decompress the compressed key?