Erase free space, can't create temp file

[can-do]

MacBook Pro (15-inch, Late 2011)
2.4 GHz Intel Core i7
4 GB 1333 MHz DDR3

Hello,
I have tried to erase free space a few times but get the message, "cannot create temporary file"
I think the message comes after some hours of apparent processing, not at the beginning when (i think)
the file would be created. Ive tried apple forums but no answers there. It is not for lack of space there is 672GB available.
Love some help with this please
thanks

 

[Weaselboy]

Try a command-r boot to recovery and from there run Disk Utility and do a repair disk. Does that find any errors?