How to install plugins in after effects cs5?

I can’t find a video on utube on how to install plug-ins for cs5 some 1 help when i put the plug-ins folder into the plug-ins section the don’t work and iv’e tried putting them in presets to plox help i’m trying to install Twixtor and Twitch :interrobang:

serious ? there is a folder called plugins, im not sure but maybe you put them in there ?

When I start up AE it give me this error "There a multiple copies of plug-in effect “Motion Vectors: Create”(It also says “Twixtor”) on your drive. To avoid problems, quit After Affects and move or delete the older or unneeded version(s)."
iv’e deleted all of the custom plug-ins and it doesn’t show the error but when i put Twixtor or Twitch it gives me that error