Validating Input Form & Saving Issue

Hi all,

I've added the below code to the nms:newOperation Input Form to check that a custom field is not blank when creating a new Campaign. I've inserted the code inside the form but outside of the container. It is giving me an error if the field is blank (working correctly), but then upon inputting the required field and selecting OK, the new campaign window closes but is not created. Any help would be greatly appreciated!

<leave>
    <check expr="@audienceLevelId!=''">
        <error>Mandatory field - Please select Audience Level ID</error>
    </check>
</leave>