I just remembered after making the post, it was the same when I was first playing this game. My caterpie got hit by poison sting and it was super effective, but I just want to get a confirmation :P Thanks :)
Sludge and sludge bomb is super effective against Heracross, can you verify why this happen. It's occured when I was doing DC today. Don't know about other poison type move. Thank you.
Is that the process you see on task manager which is "PWO.exe"?
If all the above method still doesn't work, try to reinstall your OS. After that don't install anything yet and install PWO client and run it.