After filling in the Send transaction screen and entering a correct password when you click on Send you get An Error Occurred message.
The problem is caused by using a invalid address.
If you try to send funds from Mainnet to a Testnet address that will trigger this error. Likewise, if you are using the Daedalus wallet testnet client to do some testing and you try to send ada to a Mainnet address that will also trigger this error.
Check that the address you have used is from the correct network.