Adding Drive - Size Is Wrong

Hi

I am attempting to add a drive to my WHS.  I currently have 2 x 500g IDE drives and a 1TB SATA.  I have just installed the new drive, (a 3TB SATA), gone to the server storage tab and found my three existing drives plus the new one with the new one showing as "Not Added". 

Problem is the WHS is reading the new drive as 746.51GB.  Shurely Shum Mishtake! 

Can Anyone suggest what might be going on and how best to sort it?

Thanks

M