In case you missed the change, Xojo no longer creates apps that run on Windows XP.
In fact, the last version of Xojo to run on XP was 2013r3.
Starting with 2015r3, Xojo no longer creates apps that work on Windows XP. You now have to use Windows Vista, Windows 7, Windows 8.x or Windows 10.
Note: Also starting with 2015r3, Windows Vista is deprecated. This means support for it will be removed in a future version of Xojo.
By no longer maintaining XP support, we can move forward applying newer Windows technologies to the Xojo framework. In fact, 2015r3 has two such improvements: one to threading to reduce CPU usage and another to use the newer Open/Save/Select Folder dialogs style.