We've had the same issue in our Trust. The machine had DLP 126.96.36.1992 and McAfee Agent 188.8.131.529. We had the device itself excluded in the Device Definitions and Policies. When the user tried to mount in TrueCrypt, it would hang and never respond again. You'd have to shut the machine down (cold boot).
Now that I've taken DLP off completely, he can mount and dismount with TrueCrypt fine.
We did have some problems in the past with 9.0 versions (totally separate from this issue) so the user and I will probably put 184.108.40.2062 onto the machine and see if it gets the same results. And I'll bring his agent up to 220.127.116.110.
If anyone has some insight to this, I'm sure we'd be most grateful.