Well, like it says, you've got a LOD problem.
You only updated the model in the first resolution LOD (the ones with numbers, lowest number = first lod), so it won't show in the others.
I suggest looking at the right hand side of your screen in O2, you'll see a box with several entries, like so:
0.350
0.750
1.000
1.500
Memory
View - Pilot
It should look something like that for a weapon addon.
Now, you've only updated the model in one of the "number" LODs. You need to double click the rest of them and update it there as well.