Error notification when trying to verify Electrum Sig...?

An error occurred: Kleopatra: Could not open file "C:/Users/User/Documents/Crypto/Electrum/electrum-3.3.6.exe.asc" for reading: Input/output error (218136625)


Basically - downloaded the electrum installer and signature file to the same folder, imported the thomasV public key - then clicked "verify", selected the electrum sig file - and that's the response.

I'm concerned about transferring coin to a wallet that's not verified.

Is this a common error?

Am I making some obvious mistake?