installing Bitlocker on Raid 5 drives

hi thanks in advance for reading this.

i am trying to install BitLocker on our servers:

PowerEdge R900

4x 6core

128Gb ram

5 x 2Tb on Perc 6/i

configured as Raid 5 no spare 3 partitions 1x 350Gb system 1 x 4tb (GPT) 1 x 3.2 (GPT)Tb data, 

BitLocker runs fine on partition 2 (4TB) but won't run on partition 3 (3.2TB)

any ideas ? have tried re-partitioning still the same