Function burnfrom error: gas required exceeds allowance or always failing transaction

Question

I have created a contract using Remix.

When I run the function burnFrom(), it shows:

gas required exceeds allowance or always failing transaction.

What am I doing wrong?

function burnFrom(address _from, uint256 _value) onlyOwner public returns 
(bool success) {
    require(balanceOf[_from] >= _value);                
    require(_value <= allowance[_from][msg.sender]);    
    balanceOf[_from] -= _value;                         
    allowance[_from][msg.sender] -= _value;             
    totalSupply -= _value;                              
    emit Burn(_from, _value);
    return true;
}

Answer 1

Check that you are either using the javascript VM or that you have metamask unlocked and connected to a test net if using injected web3.

Make sure you have an allowance mapping that looks like this:

mapping(address => mapping(address => uint256)) public allowance;

And that your Burn event looks like this:

event Burn(address indexed from, uint256 value);

If you have both of these correct there is probably something wrong with the onlyOwner modifier.