Hard disk full but not really

Hiya,

So my friends and I are using her account to play sims and I've downloaded the game before on an external hard drive because my mac doesn't have enough storage to download the game and all the expansion packs. I just went to download sims Realm of Magic onto my hard drive but the game wouldn't download so I uninstalled sims hoping maybe it would help. Take note my hard drive has over 750 GB of free space on it, I've used the hard drive to download the game onto it before so I know it works but now when I try to download the game onto my hard drive it won't work and comes up with a message saying my hard drive is full and I need to clear space. I've cleared space on both my mac and the hard drive, tried restaring my laptop and reinstalling origin but nothing is working and I'm getting really frustrated! Please help!