You don't give us much details mate...
- How do you use your CF card? Via PCMCIA adapter or via CF 2 IDE adapter?
- How did you prepared your CF for Workbench usage?
- What filesystems are you using?
- What are the Max Transfer/Mask/Blocksize you're using?
- What brand and what capacity is your CF card?
- What partitions have you declared and at what size?