DVI Ouput resolution at 1024x768 for AM3517 EVM

Hi,

    I face a problem about dvi ouput setting on AM3517 EVM.

    I do this procedure

                 target $ echo 0 > /sys/devices/platform/omapdss/display0/enabled

target $ echo "" > /sys/devices/platform/omapdss/manager0/display

target $ fbset -fb /dev/fb0 -xres 1024 -yres 768 -vxres 1024 -vyres 768

target $ echo "dvi" > /sys/devices/platform/omapdss/manager0/display

  At last command, i get an Error Message ->  

              omapdss MANAGER error: failed to set manager

  But when i change command,it wouldn't get any error?

             target $ fbset -fb /dev/fb0 -xres 640 -yres 480 -vxres 640 -vyres 480  

  Does it not support resolution for 1024x768,

  I use AM35x-OMAP35x-PSP 03.00.00.05  , rebuild kernel (not add patch) and NFS filesystem 

  How can i resolve this problem ??

Best Regards,

Mark