Removing a Hard Drive Partition - "The requested change in size is too small"

I am trying to delete a bootcamp partition using Disk Utility and when I try to do so, the error "The requested change in size is too small" comes up.

The partition is 160 GB, so I don't understand how that could be the case.

FYI: I am on a 15 in Macbook Pro running 10.8.3.

Any help would be appreciated.