RadGrid Update Validation

[William]

I have a RadGrid which when editing a record opens a Pop-Up edit window. Within the edit window is another RadGrid. What I would like to do is validate that any changes to that embedded grid have been saved prior to allowing the record to be updated. In my ItemCommand "Update" code I can tell if the embedded grid is still in edit mode or not, but I'm not sure how to prevent the Pop-Up edit window from closing. Attached is a picture of my scenario, perhaps that will be easier to understand.

Thanks.