InfoPath Dev

I'm trying to use an InfoPath form to create a new list item and one of the fields that I'd like to have it populate is a Lookup field. The intent is to set a value for the Lookup field so that related columns/fields will auto-populate based on the Lookup value. (Ie. My lookup column is MemberID and I'm trying to retrieve data from a list containing demographic data. It works/auto-populates when I add items via DataSheet view.) That said, when I try to submit the entry, I get a red-dotted box with error message indicating "Only positive integers allowed".

I'm guessing this is a SharePoint list form?

For your lookup column, you have to set the field to the list item ID for the item that is being looked up - so, let's say this is your "Employees" list and you have a lookup column to another list called "Departments" - you will need to set the field for that column to a valid Department ID - does that make sense?