A: If anything changes around the boot configuration of your machine, BitLocker prompts for the recovery key before you can continue using the machine. (By the way, many actions can cause changes to the boot configuration, including BIOS updates; find a full list of causes at the Microsoft article "BitLocker Drive Encryption in Windows 7: Frequently Asked Questions.") 

To fix this, after you boot into Windows, you must suspend, then resume, BitLocker. This resets the boot information and avoids the need to enter the recovery key again. To suspend, then resume BitLocker, do the following:

  1. Open the BitLocker Drive Encryption Control Panel applet (Start, Control Panel, BitLocker Drive Encryption).
  2. On the C drive, select Suspend Protection.
  3. Click Yes to the confirmation.
  4. Select Resume Protection.

You should no longer be prompted for the recovery note. Ideally, you should actually perform the BitLocker suspend action before making changes to BIOS and disks, then resume Bitlocker after you've made all your changes. That way, you won't have to enter the recovery key at all.