What version of Electrum do you install?
Are you sure that you download that Electrum from the correct URL? it must be electrum.org

There are many fake Electrum wallet out there and maybe you use the fake one that is why it can't decode the wallet file that generated from original Electrum wallet.

Yes, of course, it is the correct URL and the original Electrum.

run electrum and enter a unique filename in the window that pops up. then go through the process of restoring your wallet file. note electrum only supports bitcoin.

The problem is that Electrum is not able to read the restored wallet-file. There is the error message I quoted in my first post.

Try HCP suggestion first, if your wallet isn't encrypted, all you need to do are finding your private key/master private key and import it to Electrum (by creating new wallet).

If it's encrypted, try find other backup (either wallet file or mnemonic/seed/recovery words) you might have.

Sounds like the wallet file is corrupted after the restore.

Are you sure that it is an Electrum wallet you have restored? Was it encrypted? If not, have you tried opening it with a text editor to see what the contents look like?