Assuming you haven't upgraded your electrum client like nerioseole asked:
This command will rename your configuration file to to configuration.bak so that Electrum will make a new configuration:
mv ~/.electrum/config ~/.electrum/config.bak
Next you will want to open Electrum.
It will ask you to import or create a wallet. The importing option only allows for wallet recovery using the seed. Since we want to import your old wallet from a file we just go ahead and create a new wallet so that we can get past this screen. Go ahead and make a new wallet.
Once you have Electrum open like normal, select File, click Open wallet. Your wallet should be there. Select it. Click ok and you should have your wallet back.
If that didn't work for you let me know
Handy hint. Files starting with . are considered hidden. Push ctrl + H to show them.