Computer only allows me to create a 4.00 GB Disk Image?

I am trying to create a disk image with disk juggler, and
also with Nero and I can't create an image bigger then 4
GB big.

With Disk Juggler it creates a 3.99 GB image and then
causes an error that says "NOT ENOUGH SPACE ON DISK" and I
have plenty of Hard Drive space left.

With Nero it creates a 4.00 GB image and causes no
errors. Says it ends successfully but just quits.

I was just wondering if anyone had any ideas what could be
causing this problem to occur?

Thanks for your help,
Patrick