When I first bought a T540p, I also got a solid state drive (Crucial M500 series) to install in it. Even though the drive and the T540p meet the requirements for eDrive1, it initially would not work. After doing some searching online, it turns out, that the Lenovo preloaded install was the issue, and performing a fresh install of Windows 8 allowed BitLocker to use the M500’s built in encryption.

  1. There is an Anandtech article detailing requirements and setup, as well as Microsoft Technet information.