This deserved a better reply. I could not figure out what you meant by going to Tools > Default Values and had to go to another site, which explained it better:
http://sharepointfruity.blogspot.com/2012/12/error-fix-selected-control-cannot-store.html
Maybe some things have changed since 2010, as I'm using InfoPath Designer 2013. Basically, you go to the Data tab in the Ribbon, and click "Default Values" in the Form Data section. From there, you find the misbehaving field and check the box beside it. Apparently these are the fields to include when the form is a "new form", though I don't really understand how InfoPath makes that distinction. But checking that box is what fixes it.