error when downloading configuration

Hi, all:

I meet with a problem.

Error occurs when I am downloading the .sof file in jtag mode with usb-blaster.

Error Message: Error: Can't access JTAG chain, Error: Operation failed

Two print circuit boards(PCB) are used. One is stratix II ep2s60 development board and another is Peripheral Circuit of the stratix board. They are connected though Pin header. I have found that error occurs when the boards are connected. Once they are disconnected, downloading .sof file will success.

And I am sure the corresponding places of pins for jtag on the development board are not used in another PCB.

What's wrong with my project? and what can I do then ? My project requires both of the PCBs, otherwise the system cannot work correctly!

could anyone help!