Basically, I made a pair of shoes, and following nightasy's tutorials to the letter have worked all other times(top, hands, legs), but maybe I did something wrong, because it doesn't rig properly anymore.

My shoes don't "move" with the skeleton, instead they "slide" with my character's movement. I don't know why it's doing this.

I use 3DS Max.

I've tried re-exporting twice.

Solved this by adding the shader1 flag SLSF_Skinned..

It's amazing how one missing flag can ruin a whole nif file.