I looked at the "Mercedes_2012_WSM.vmx" file and all it should need is to change the line virtualHW.version = "8"tovirtualHW.version = "7" and that should do it for the configuration file. You can open it in Notepad to change it.
The "Mercedes_2012_WSM.vmdk" file might also need to be edited and the following option and its value should not be higher then this: ddb.virtualHWVersion = "7"
Again, you can open it in Notepad to change it.
Obviously, backup each of these files before editing them! 