Problems when erasing free space

Hi guys,

A pleasure to meet you all =).

I'm writting in the forums because I have a problem when trying to erase the free space I have in my HDD. When entering the disk utility, and I try to erase the free space in my HDD, even with the fastest option, when it's about to finish an error message appears saying that it has failed because it isn't possible to create the temporal archive.

Hope you can help me. By the way, sorry for my traduction, I have my mac in catalan so I'm translating the messages.

Thanks and have a nice day =)