Bootcamp Deletes itself, Cant remove partition!

Hey,

My Bootcamp was running perfectly well for 6months straight as it was installed a while ago but then suddenly without me doing anything all of the Windows install files/directories have disappeared.

So I decided to look it up and every forum comes up with needing to remove the Bootcamp partition and install Windows from the original DVD as when it was installed before but when I go into the Bootcamp Assistant application it comes up with

"The startup disk cannot be partitioned or restored to a single partition. The startup disk must be formatted as a single Mac OS Extended (Journaled) volume or already partitioned by Boot Camp Assistant for installing Windows."

With the only option to proceed as "Ok", I click the button and I see Create a Windows 7 or later version install disk, Download the latest Windows support software from Apple & Install or Remove Windows 7 or later version as shown below: