Failed to initialise TPM error

If you get an error (0x80070005) when initialising TPM for Bitlocker and you have GP set to 'Save the recovery key to AD' then make sure the computer object has Write permissions to itself in AD.

Enabling PIN at startup when Bitlocker is already enabled

If you have Bitlocker already installed on your drives but would now like to require a PIN at startup, follow these steps:

1. Check Group/Local policy (Computer Configuration > Administrative Templates > Windows Components > Bitlocker Drive Encryption > Operating System Drives)
2. Make sure that 'Configure TPM startup PIN' is set to 'Require Startup PIN with TPM' in 'Require additional authentication at startup'
3. Suspend Bitlocker
4. From CMD, run 'manage-bde -protectors -add c: -tpmandpin xxxxxx'
5. Reboot and it will prompt you for the PIN you specified.

Enabling disabled Local Admin account in Windows 7

Even if Bitlocker is enabled.

http://www.grouppolicy.biz/2010/10/how-to-enable-a-disabled-local-administrator-account-offline-in-windows-7-even-when-using-bitlocker/