Switching gears sets "gear not found"

[Kmt]

Thank you to you both for your replies,they will prove to be a great help.
However when i reloaded my leather worker today,i had the same message come up.
Same thing again a item had gone from the set.Not materia but belt i had on his waist.
I have made sure that all gear sets are fully equipped but still get this problem.
I know it is something i am doing wrong but not sure what.Is it the way i am converting items into materia?
I take them off and put them into armory then convert.
I also make sure i have an item ready to replace it in my inventory and replace it from there.
Thanks in advance for any help.

[Niwashi]

Is it the way i am converting items into materia?
I take them off and put them into armory then convert.
I also make sure i have an item ready to replace it in my inventory and replace it from there.

Be sure to equip the new item and update the gear set (triangle on PS3, I think it's a button to click on PC) before converting the old item. Also, make sure you do that update on all gear sets that use the item. (This is the part that usually catches me.) For your leatherworker belt example, do you have other crafting classes that may have been using the same belt? Perhaps you updated one of them and then converted the old belt, without realizing the leatherworker set was using it as well.

Before getting rid of an old item, make sure it's no longer used in any of your gear sets. Any item that's part of a gear set will have a little page symbol in the lower right corner of its icon. Be sure there's no such symbol on it before converting, removing, or selling gear.