Vista - Readyboost problems

I managed to set up ready boost on one of my USB flash drives. After that I
turned off the laptop and removed the USB flash drive. When I turned on the
laptop again, I couldn't set up again the READYBOOST. It keeps saying me that
"A cache exist
on another device in the system" , when actually I don't have anything else
connected. I tried with different flashdisks, I tried with SD card, I tried
to retsrat the laptop, to format the flash drive, but nothing seems to work.
Please help me.