Problem enabling drivelock on HP notebook

I want to enable HP drivelock for our colleagues. They are using HP 4540s notebooks. We upgraded the default hdd to a new ssd. Then we tried to enable the drivelock password. For most of the users that worked. But some get the message "HDD is HW encrypted" and they are not able to set a password by any chance. They all have the same SSD, but some work, some don't, I don't get it ... They are all running on Windows 7 x64 Prof. as OS. We are using Crucial M500 SSDs.