Please have a look on this issue : ethereum.stackexchange.com/questions/42122/declar…

browser/mycontract.sol:64:27: DeclarationError: Identifier not found or not unique.
contract StandardToken is ERC20, BasicToken {
                          ^---^

browser/mycontract.sol:64:34: DeclarationError: Identifier not found or not unique.
contract StandardToken is ERC20, BasicToken {
                                 ^---^