Hi,
One situation where this might be the case is where the ADUC7126 is in a kernel (or serial) download mode. You cannot talk to the part via JTAG in this mode. This can be entered or not depending on the state of a particular pin after a reset. I'd be checking that now, I can trigger these error messages if I place the device into the download mode.
P0.0 is the boot mode pin on the AduC7126. If this is held low at a reset time then it will be in the download mode and you not be able to connect via JTAG.