@jagabo, sorry I didn't get any notification. Yes, those registries make much more sense, unfortunately it didn't solve the issue.

I went ahead and decoded the jpeg using AvsPmod x86, that was fine for my deblock benchmark but bad because I know that at some point I will need to use a certain x86 plugin. My tests were done with the minimum plugins and scripts included in the plugin folders as shown on my above post.
After fixing the registries I guess now the ball is on the MP_Pipeline roof, but for the time being I will let it rest and battle it in the future.

@poisondeathray: It's not complaining about ConvertStacked.dll it just happened to be the first plugin it found (alphabetically), because it's searching in the wrong folder.