I had the opportunity to ask someone from the hardware team at Microsoft
about this. It is a well known problem with the M5 they have come across
internally. Here is what he said:
---
:

uring Toshiba Tecra M5 there was a transition from Intel Core Duo
processors to Intel Core 2 Duo Processors. All systems coming with Intel
Core 2 Duo processors were released after the final TPM/BitLocker
specification was released, therefore their BIOS included the right
Boot-block and EC/KBC BIOS firmware (this is different from the normal
BIOS).::
::::
::In order to make systems with Core Duo procs to work with BitLocker,
you need to flash a new Boot-block and EC/KBC BIOS firmware in addition
to the normal BIOS.::
::::
::It's easy to find out if a system has Core Duo or Core 2 Duo
processor... you only need to take a look at the msinfo32 information
for each system. If the processor is a T2xxx family, it is Core Duo; if
it is T7xxx, then it is Core 2 Duo.::
---
In other words, to get an M5 with Intel Core Duo to work with
Bitlocker, you need an additional firmware update as well as the BIOS
update. Toshiba do not publish this extra firmware - it's not available
on their site for download.
I have spoken to Toshiba support about this. They suggest sending all
80 of our Tecra M5s to an authorised support provider who will carry out
the firmware update for us and return them.
This is useless from our point of view - the 80 laptops are currently
in the hands of 80 staff driving all over the UK. What we really want is
the firmware so we can apply it ourselves.
--
matthewj9