sdram tunning

hi

I use EP2C20Q240C8 with a 32 bit sdram

when I use pll number 2 (pin 177 is pll_out

that connected to sdram clock and pin 178 is

connected to sdram clock enable . Nios 2 program

is verified but the program doesn't execute .In the

other case when I use pll number 4 and sdram clock

is pin 177 and sdram clock enable is pin 178 Nios 2

program execute .Why the pll number 2 doesn't

work.I test this problem for variety of pll phase shift.