I have got the same problem with the same uC and TBDML. But when i try to unsecure I get error when 39%, 78% and 93% are loaded and a message that "Derivate could NOT be unsecured!!!!
The unsecure command file might be missing or disabled.
Make sure the command file defined in the unsecure panel of the command file dialog contains the correct commands to unsecure the current connected derivative and the board oscillator frequency."
I have tried different unsecure.cmd files, among others the one mentioned by daporta but no one works. I have set the frequency to 8MHz for target and the ratio to 1.33 (TBDML = 6MHz) and even tried the recommended 2.00 ratio. I have set the correct derivative to MC9S12C64.
Any ideas what may be wrong?