help, Programming flash error!

in my custom board, i can read the flash and can not write to it ,following is the information when i use the flash Programmer:

# ! /bin/sh# # This file was automatically generated by the Nios II IDE Flash Programmer.# # It will be overwritten when the flash programmer options change.#

cd D:/altera/kits/hello_world_pll/Debug

# Creating .flash file for the FPGA configuration

$SOPC_KIT_NIOS2/bin/sof2flash --flash=U2 --offset=0x0 --input=D:/altera/kits/cy1

2pll/cy12pll.sof --output=cy12pll.flash

Info: *******************************************************************

Info: Running Quartus II Convert_programming_file

Info: Command: quartus_cpf --no_banner --convert D:/altera/kits/cy12pll/cy12pll.

sof cy12pll.rbf

Info: Quartus II Convert_programming_file was successful. 0 errors, 0 warnings

Info: Processing ended: Sun Oct 15 18:08:18 2006

Info: Elapsed time: 00:00:00

WARNING: Default charset GBK not supported, using ISO-8859-1 instead

# Programming flash with the FPGA configuration

$SOPC_KIT_NIOS2/bin/nios2-flash-programmer --input=cy12pll.flash --sof=D:/altera

/kits/cy12pll/cy12pll_board/system/cy12pll_board.sof --base=0x01000000

Oct 15, 2006 6:08:20 PM - (??) nios2-flash-programmer: Launching Quartus Program

mer to download:

D:/altera/kits/cy12pll/cy12pll_board/system/cy12pll_board.sof

Pre-Reading 283KBytes of data from U2:

|----.----+----.----|

********************* (13.125 sec).

Erasing 5 Sectors:

|----.----+----.----|

********************* (2.922 sec).

Unable to send write-packet @0

buffer-chunk write failed @0

erase-block write failed @0

write failed @0

Oct 15, 2006 6:08:51 PM - (??) nios2-flash-programmer: Unable to write to flash

Oct 15, 2006 6:08:51 PM - (??) nios2-flash-programmer: Error: Write-operation fa

iled on device. - exiting.

the flash is AM29LV128ML-123REI, and i use the preset flash parameter in SOPC Builder,the osc is 50Mhz,wiht Q5.0, i have also examed the board several times and the connection is ok ! please help me,thanks!