BitLcoker Problem

I have installed Vista on a single partition. I have created a second primary
partition (2GB), made it active and made it system partition. Vista now uses
the second System partition and boots w/o any problems. The problem is when I
go to Control Panel to activate Bitlocker there is a Warning saying that the
system is not read. The computer is Dell Latitude D420, with TPM activated
and initializied, with BIOS updated to the last version available on Dell web
site. When a command line (manage-bde.wsf -on c: -rp) is used to activate
bitlocker averything works perfect!? Any idea why BitLocker cannot be
activated via GUI? Thanks