I have been working on trying to crack my own WEP network for sometime, and I am finally stuck.

For reference, i'm following this video exactly, as I have the same wireless USB router,
YouTube - Crack wep with backtrack 3

I have tried collecting various amounts of data, from 12,000 all the way up to 40,000
and I am still running into the same problem

Everything goes fine until I try aircrack-ng

I open up the new shell, type in everything i'm supposed to, hit enter, then it waits a few seconds and says "killed"

Can someone please help and point me in the right direction.

FYI, i'm using backtrack 3 on vmware and my router is compatible