Difficulty in partitioning HD for installing Windows

I am attempting to install windows using bootcamp and windows 8.1. I have a MB Pro 13inch, no optical drive. I have made an .iso version on another computer, saved it on my MB pro, plugged in an empty flash drive, 16GB, and continued with bootcamp assistant, and constantly get the message when getting to the partitioning of my HD, that files can't be moved in order to create the partition. Disk utility says that my HD is the appropriate format (single partition, Mac OS extended (journaled), I have verified the disk, and even reinstalled OS X, then repeated the process of using bootcamp, still with the same error message, that I can't partition the disk and files have to be moved! How do I get around this one?