Bad hub or stupid rider?

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I recently bought a "economy" wheel for my fixed gear conversion bike (I had been running singlespeed (one cog and a bunch of spacers) on the same frame). I spun a track cog on and the lockring and put the wheel on my bike. I went out in my neighborhood for a spin and managed to strip the hub within about 20 minutes (39x16). It looked like just the area next to the spokes themselves was stripped, so I put a spacer over that area, reassembeled the whole thing and rode around again. As I was standing on the pedals to go up a really steep hill the whole thing stripped out again and this time the hub was toast. I can't even get the cog off it is so mangled.

So, what next? Was it the "economy" hub? The "economy" cog? Did I not tighten it enough? Did I tighten it too much? It would be great to get some ideas before I go about acquiring parts to try again.