Hi, I had the same problem. I red the comments down here and thanxs go-d I succeded to solve mine.
hopefuly to solve yours and others, too.
I've got a standard SanCruzer 32GB
formatted it to FAT32 file system and now the WorkCentre 6027 recognizes the flash drive and let me print from it.
I must say that at the beggining I formatted the flash drive to FAT32 but it still didn't recognize the drive until I formatted the partition under it, too to FAT32 file system (before it was formatted as Exfat and didn't work).