I rebuilt the MFG Client driver (iMX28-EVK-PDK1_9-UUT), and renamed the nk_ivt.sb to uce_ivt.sb, then copied it to "mfgtools\Profiles\MX28 WinCE Update\OS firmware".
When I used this new uce_ivt.sb to update my firmware(eboot_ivt.sb, nk_ivt.sb) and file(sandy.mp3) to SD/MMC, I found MFG client driver didn't create MBR section in SD/MMC, so it can't write the file(sandy.mp3) to disk.
BUT if I use ORIGINAL uce_ivt.sb in the "mfgtools\Profiles\MX28 WinCE Update\OS firmware", it works fine.
So I don't know why my built uce_ivt.sb can't work? I don't change any configuration of iMX28-EVK-PDK1_9-UUT, I only SYSGEN it in the first time.