Did you do full unprovisioning before trying to re-provision it to the other mode?
For resetting the system to defaults, please disconnect the power cord and LAN cable. Remove the CMOS battery for 15 secs and insert it back in. This time when you power on, ME settings will revert to factory defaults.
Also, make sure that you have the latest firmware installed on your system.
Did you try to contact your OEM?
If the un-provisioning and re-provisioning through bios settings don't work, the only waythat I could think of isto take off the CMOS battery to reset the system to factory deafults and this should work.