Our IS told us today that we could go ahead and use our old software for the time being. We've been told previously that we couldn't do this. I hope the most recent advice is correct. :-)
The issue may be in the clearinghouse.
If your information has been transferred to the new clearinghouse, the old one MIGHT reject your claims. Perhaps they could be forwarded to the new clearinghouse but you probably need to know which one is active (and for which payors.)
You may be able to change clearinghouses in medisoft, but I have no idea how difficult this may be.