Not enough space. I have 20 gigs of unallocated space?

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http://forums.fedoraforum.org – So i have 20 gbs of unallocated space on my hard disk. I get this error when i try to install fedora using the "Use existing space" Option. Shouldn't it create a new partition automatically? I have 400 gigs on my C: drive, and 20 gigs of Unallocated space. Why doesn't this work. My theory is that this isn't truly unformatted space like i need. It says it's unallocated though? So apparently you can only have four partitions. Is this true? In that case i can't install it? Here's a picture of my disk management. [2] http://i.imgur.com/fCbmh.png what should i do? (HowTos)