It has been awhile since I had my D1 but I seem to remember being told to put the disc in the machine, transfer the design to the machine screen and then take the disc out-something about the disc getting too hot if you leave it in all the while you are embroidering. Hope this makes sense,maybe a HqusvarnaViking dealer could explain it better.
I've never had this problem (I use 3D Pro) and have no idea why that should happen. Have you tried using a new disk? After a while they no longer work as they should, although I mostly get a 'disk not recognised' or a 'no disk' message with old disks. Sorry I can't be of help.