InfoPath Dev

Thanks Hilary, I did work it out in the end and that's the validation rule I ended up with. Thanks again, I can see this site being a real help as I go forward in using InfoPath.  

Hello, Please help a frustrated new user to InfoPath 2010! I've created a form which has a header and three sections. There is a drop down field called "Action" in the header which when a certain value is selected the relevant section will be shown. In these sections I want to force a date field to be populated by setting a ...