Trouble partitioning hard drive- not fragmentation?

Hey, i'm trying to partition my Mac's drive using bootcamp so that i can install windows on the new partition. Boot camp comes up with an error stating it can not move certain files. I have the demo version of idefrag and it shows that i have a huge section of continuous empty memory, so fragmentation does not seem to be the problem. I have only owned this machine for 6 months and less then 50 gb of the 250 gb drive have been used. Any information would be useful, but i would prefer simple solutions, if there are any, because i'm not exactly a pro. Thank you, i appreciate all help.

I also got this problem when using Boot Camp. What I did to fix it was repair the hard drive. To do this you have to boot using your OS X disc that came with your computer and then hold down C on restart. Once that's done open up Disk Utilities in the menu. Select your hard drive and click on repair disk. Restart your computer once that's done. It may or may not solve your problem but it worked for me.

Air

What if you're using MacBook Air? It does not have original CD. I am struggling so much with it

To commence BootCamp Assistant and install Windows, the drive needs to be formatted Mac OS Extended (Journaled) and in one single partition. Check Disk utility out as suggested and if you have a MacBook Air run Recovery and check the drive that way.

Then print and study BootCamp Guidelines before starting the install. Download drivers and burn to a CD.