A secured device cannot be accessed via JTAG. Otherwise this would be a security hole.
You have to use the Burn-In ROM bootloader features, by using the tools USB direct programmer or MCU Flash Programmer.
On both, you have to connect first (button download) and then Erase. After Erase you have to perform Erase.
If you do not see enabled the erase button, then you have not connected by using the download buton (download referes to downloading a kernel that is needed)
thanks for the info. I've figured it out what I was doing wrong. Reseting the device during this process seemed crucial. This while leaving the power on the module and the bootloader activated.
Thanks for the feedback. Happy to read that it works now. #Holger