Make sure your old receivers are unplugged when you swap the LNBFs. Be especially careful if you are switching from DishPro to Legacy - either to a Legacy Quad from a DishPro Twin (probably not a dual), or if you're going the other way to fallback.
The simple procedure, is to ALWAYS do a Check Switch with NO feeds connected, followed by a power-plug reboot and another Check Switch whenever you switch LNBFs. It's usually overkill, but always safe.
Note that 4-digit model number receivers will NOT work with DishPro without extra hardware.
If I have confused you with all this, either read a bunch of threads (the info is all here somewhere), or call that pro that Van and Rob suggest.