So I was playing with friends in Scavenge and I was the charger and I charged my friend over 80 feet after picking him up and it wont give me the achievement. Is anyone else having this problem? Or am i not doing something right

This has happened to me. i can only assume the charger has a maximum charge distance with or without survivor, therefore you have to start your charge toward the suvivors when you're quite close. if you start a fair distance away from them (as i did) by the time you've ran toward them and picked one of them up there isn't enough distance left in the charger to carry the survivor over 80 feet.
try hiding round corners with a clearing opposite you or running round the survivors punching them before charging away with one when your positioning is right. timing is all important with the infected given the 'recharge' time for their special attacks.

I been trying to do it in Hard rain- Sugarmill behind the water tower and then straight forward is the generator thats way over 80 feet and each time i do it i make sure they come really really close and i pick em up and charge em all the way to that generator but still wont give me it.

i'd love to try out getting that achievement if the game would stop crashing to desktop whenever i play scavenge mode -___-
 i suppose i should be thankful that my CTD's have ONLY happened while playing scavenge though.  hasn't even happened to me in campaign which is nice.
 now that i think about it though...the CTD's i've been getting were while i was playing on XP.  i need to try playing the game in Win7.
 
but yeah, i don't remember hearing about this many achievement bugs in L4D1.  hopefully valve will get the problems sorted out soon.  other than that though the game is still totally playable.

It's not really messed up. It was an error or something, keep trying.

Some of the achievements in this game are a bit iffy. Especially the ones involving the charger, like the 'melee the charger while he's running' one. Did that 3 times before I got it.

that one's particularly tricky cuz i'm guessing you also need to take lag into account which means you don't just wait for the charger to get close to you when he's in the middle of the charge.  i think you're supposed to swing your melee weapon ahead of time to compensate for lag.