Can't extend partition after burn an image

Hi,

I've created a image backup from my source data disk (30GB). After that I
"burned" this image to the target disk in the same server. The size of
target disk is 50GB. When I check the target disk size through Disk
Management I can see the incorrect target partition size of 50 GB without
blank spaces, but when check the size through Explorer I can see the correct
size of 30GB.
Then I tried to extend the target partition using Diskpart, but I get an
error saying that the partition cannot be extended!

Does anyone had similar experience or has any suggestion ?

thanks in advance,
Rubens