windows 2008 Cannot extend volume for c

I have a 150 GB hard drive on a windows 2008 server.

• 87 GB partition for D:
• 10 GB partition for C:

I cannot extend/increase the partition for C: in the disk manager utility.
as described here:
http://www.howtogeek.com/howto/windows-vista/resize-a-partition-for-free-in-windows-vista/
I tried doing it through the command:
http://www.winvistaclub.com/t11.html

However I got the error: There is not enough space available on the disk(s) to complete this operation.

Is there unallocated free space in which to extend it? You won’t be able to extend the C: drive into the space occupied by the D: drive unless you delete the D: drive.

Check more discussion of this question.

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