"ASN-EDI is already exist" is grammatically incorrect, are you certain that this is not a homemade error message where the programmer just selected a convenient way by choosing VL001 message since this is nothing else than a variable.
Go SE91, find the message, select it and click the Where-Used icon to see in which programs it is used, then check from there program by program if you can find this text.
Alternative you may want to debug the execution to see when and where this error is processed.