Send coins with Electrum from encrypted wallet created with Bitcoin Core
Every wallet can create it's own way of storing data. There's no protocol in bitcoin,that defines the way, how a wallet is structured. In your case it might be best to extract the private key, and load it into Electrum, like here:

http://docs.electrum.org/en/latest/faq.html#can-i-import-private-keys-from-other-bitcoin-clients