Crafted items cannot be used

Kanai’s Cube. Trying to convert a set item, Guardian set, so I know there are enough pieces in the set ie 3. I know I have enough materials to convert.

I have two Guardians Aversion (Bracers) which I want to convert to try and get the Guardians Case (belt) but when I hit Transmute, I get the error message “Crafted Items Cannot be Used”

I’ve googled this and can find no mention of that text anywhere. Is this a bug ??
I have no problem converting other Set pieces. It’s only this one that causes me this issue.

Can anyone tell me if I’m doing something wrong ?

Thanks

PS Playing on Switch.

You can’t convert / reforge blacksmith-crafted items.