Interfacing between cyclone 2 and M45PE80 flash

We have on board M45PE80 serial flash which is connected to cyclone 2 throughout SPI bus.

On some boards M45PE80 flash works perfectly, while on other boards it works for 1 or 2 months or less and then it stops working. M45PE80 flash not responded, although fpga cyclone 2 correctly generates timing. I was surprised when I press with finger on the

M45PE80 it starts to work again. On some boards M45PE80 never works. The changing spi bus frequency does not influence design.

Interfacing between cyclone 2 and M45PE80 flash is done according http://www.propox.com/download/docs/evbst7_disk_en.pdf( without serial termination)

Thanx, Amir