The Invalid Argument Value warning is issued in the following situations:
Unable to validate if the ‘WebReferenceName’ argument of the action ‘<actionName>’ refers a web service consumed in your eSpace because the name supplied is not a literal.: some actions have parameters that receive the name of Web Services consumed inside the eSpace. The web service name you supplied is not a literal so Service Studio has no way of validating at design time if the consumed web service exists in your eSpace.
Clicking the symbol will take you directly to the argument of the action where the violation occurs.
Consume a SOAP Web Service | About Error Messages