Send coins with Electrum from encrypted wallet created with Bitcoin Core I am totally new to bitcoin. I have google'd this a lot now. I created a wallet with Bitcoin Core GUI and encrypted it (settings -&gt; encrypt wallet...). Then I took a receiving address from the wallet (file -&gt; receiving addresses...) and sent some bitcoins to that address from an exchange (bitstamp). I confirmed with https://blockchain.info/ that the bitcoins have arrived to that address.

Now I want to spend the coins. I can't use Bitcoin Core because I don't have the resources to download the entire blockchain, so I want to use Electrum for sending coins. 

How do I import an encrypted wallet.dat created with Bitcoin Core to Electrum and send coins? If I try to open the wallet.dat with Electrum then I get Error cannote read wallet file
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