The problem is this. Any tounament your enter, you stay at the tier that you started it with.
e.g. You entered Dec unlimited as an amateur. Now any time you try to play that tournament it will be at the amateur tees even though you are now a pro.
It will not let you play when you have Pro equipment because it gives you an unfair advantage over the other players.
Any new tournaments you enter will be at the pro level so no issue there.
As of Jan 1 you will have no issue as well.
If you still want to play the amateur tournaments that you have entered you must unequip your pro only equipment.
Hope this helps.
*edit Yes you can mix and match.