Bootcamp problem cannot format windows partition

I have tried numerous times to run bootcamp to install Windows on new Macbook 13" Retina. It always hangs at the stage where windows tries to format the BOOTCAMP partition. It says it cannot format it

I contacted Apple support who said that I could use disk Utilities to format the Bootcamp partition - no I can't! I have the partition shown in Disk Utility but there is no option to format it. There is an option to erase it with NTFS greyed out and it says in the info that it is in Windows NT file system

Any ideas - I have been trying this for weeks now

I bought Parallels but that was useless - even after giving over most of the 8GB memory to Windows it kep freezing / going slow?

How do I persuade my Windows install disk that the drive - called Untitled - is NTFS and that it can install (Windows 7) on it

Very frustrated as all this worked first time on both my iMacs

Help please