Unable to query target part layou

Unable to query target part layout!!!

When I   work  with the xilinx  edk(ver8.1),  after buttoning  down the �
download  bitstream�, I want to make a bootloader from the  external flash
,but a problem still baffles me all the time, when I pressed the �program
flash memory�, here is  the context showed to me..
-------------

Performing CFI Query on the flash part(s)...Processor started. Type "stop"
to stop processor
XMD% ERROR: Flashwriter application reported an error: Unable to query
target part layout!
Processor started. Type "stop" to stop processor
Flashwriter terminating !

Done!


    What causes this problem? And What should I do to solve  the problem? 
The flash I use is AM29LV040B-70JC.