Bootcamp: your disk could not be partitioned

I get this error when I try to install Windows with Bootcamp:

"An error occurred while partitioning the disk. Please run Disk Utility to check and fix this error"

I read on the internet that this problem is often caused by the Time Machine, but I've never used it.

I really don't know how to fix this problem..

I have no other partition on my disk, tried an SOS on it but no errors were found..