I had a new laptop where I wanted to deploy Windows 7 x64 Enterprise and walked to a bug in MDT 2010. Default config.
I configured 2 partitions to use the whole disk. See screenshot. 
When I deploy the task I get the following error
He wants to format partition D. But partition D is not availably.
I ended the task and opened the PE window and started Diskpart and listed the volumes.
The strange thing was that the extended partition has the drive letter S had and it was a raw partition.
After studying ZTIDiskpart.log (X:\MININT\SMSOSD\OSDLOGS\ZTIDiskpart_diskpart.log)
I found out that there was no space left to create a 300mb partition for saving Bitlocker information.
So what did ZTIDiskpart.wsf. ZTIDiskpart.wsf gave the last partition that was created the drive letter S. This is the default letter for the Bitlocker partition. So hey wanted to format the file system with fat32. Because in my case the partition size was 200GB he cannot format the disk.
Solution:
Setting the extended partition to use 95%. Then MDT have enough space to create a 300mb hidden partition for Bitlocker.
