I'm really new here, and I'm not exactly sure what the problem I'm having is. I am trying to trade two Unusuals for a Strange Australium Scattergun. I set up the whole trade, making sure to set the correct values to the Scatterguns, but when I try to create the trade, an error message pops up that states "One of the attributes you have specified was invalid". I tested, and I am sure that the Scattergun is causing the problem. The attributes I gave it are as follows:

Quality: Strange
Craft/Series/Level/Medal: N/a
No Effect
No Paint
Craftable
Not Gifted
Australium
No Exterior

Anyone know of a way to fix this?
Thanks!