Hi Andy,
Weird. Are you sure you're using the new form? There is a cache for the form templates. You can remove the old cached copy by going Start->InfoPath, selecting All Forms in the left Form Categories pane, clicking on Last Used column to find the most recent forms. Select the one you were using and click Remove This Form in the right Form Tasks pane. Now try again.
If that still doesn't solve the problem, it's likely something to do with the manifest... which would indeed be weird. In the Designer, you can go to File->Extract Form Files and save to a directory. Then open the manifest.xsf in notepad and examine the data connections. Be careful not to make manual changes or you may not be able to open your form. Tell us what you find there.
Good luck!
Patrick Halstead [InfoPath MVP]
InfoPathDev
Patrick Halstead
Project Manager at Qdabra