Geck and Weapon Models

[Campaigner]

Hello, I recently figured out how to rip NPC limbs off of their model and place them into a weapon. For this example, I used a Laser Gatling Sentrybot and a Laser Rifle. I took the laser gatling arm, pasted it onto the rifle inside of its BSFadeNode, where all the other parts are listed under, and I made sure it's not inside the firing mechanism or any other animated area. The file saves fine at this point, so I go to GECK to load it into a mod. Upon loading it into the model so that I can see it sitting on that plane, I can't see it; nothing loads. I select the nif file again, and make sure I don't hit cancel, but it still shows blank, despite it saying it has the file loaded. Must be a visual glitch, I thought, so I go and do all the other necessary preparations to include a new weapon. I save the mod, and go into the game. I can loot it just fine, and equip it just fine, but as soon as I exit the pipboy, the game crashes to the desktop. I go into Nifskope and see if I can tinker with the parts, but everything is just how I wanted it. I go to save and make sure it's saved, but the following error pops up:

 

"failed to write nif file " "C:/Program Files (x86)/Bethesda Softworks/Fallout New Vegas/Data/meshes/weapons/2handrifle/SentryLaserRifle.nif"

 

I cannot change anything about it, as the above message keeps happening. What can I do to fix this and have my weapon showing?