Partitioning failed (Mediakit error)

[GXGOW]

I've cloned my Mac hard drive (250 GB) to a bigger one (500 GB) using HDClone. I saw that it has partitioned the hard drive, so I tried to extend the partition, but it doesn't work. It said it was completed, but nothing changed. When I try to extend it to something between 250 GB and 500 GB, I get this error:

Partition failed with the error

Mediakit reports partition (map) too small.

I've tried to partition the drive from Unibeast, but I get the same errors. Can anyone help me to solve this without losing my data and (eventually) without having to reformat my drive?

 

[GXGOW]

It won't let me extend the partition over the unallocated space :S

EDIT: For some reason, it worked now by using just Disk Utility. Thanks for the help