When loading an InfoPath form from an intranet/Sharepoint etc, the form template is downloaded and cached locally. Sometimes after the template has been upgraded on the server the local client doesn’t always get the upgraded form template but uses the local cached copy instead.
You can rectify this by clearing the local cache;
Infopath /cache clearall
Verify that the cache has been cleared by navigating to the following folder for XP+
C:\Documents and Settings\[User]\Local Settings\Application Data\Microsoft\InfoPath\FormCache2
Or for Vista;
Underneath the FormCache2 folder there will be a folder with a GUID name, check inside here, it should be empty, apart from a file called _SCVer.dat.