If P0.3 on the ADuC7024 is configured to have the ADC_BUSY function could this cause JTAG access to be locked out, as that pin's function is also JTAG TRST?
Since doing this I get the following message from a programmer "TCK(pin 9) low, but should be high. Please check target hardware.".
If locked out because of this, I assume the only way to recover is to perform a mass-erase with ARMWSD.
The nTRST is an optional pin on the JTAG port, and should not cause you connection problems if you reconfigure it for other uses.
Just in case, I quickly tried this out with ADCBusy and did not experience any problems afterwards.
Doing a mass erase will remove the code on the part, and allow you to try again whatever the situation.
The message regarding to TCK was as mentioned in this discussion :http://ez.analog.com/message/13586#13586, although I'm not sure how you would 'change' JTAG pins.
I issued a mass erase instruction (07 0E 06 45 00 00 00 00 00 B5) after syncronising timing (0x08) and then tried to reconnect with JTAG and got the same message with TCK.
I ended up replacing the ADuC7024 on the board and starting again.