JTAG chain Error

Dear all,

i have a custom board, with stratix II, and Cyclone II,

till today i dont have any problem in downloading code, and debug with JTAG port,

but today i got "Error: Can't access JTAG chain Error: Operation failed" , when i try to program,

programmer is working with other boards, and all fine,

only this 2 board, does anybody have solution, if i have to correct the board. and work for

jtag

regards

baba