Cannot Extend VM Partition After Converting (Very Urgent)

Hi!

I converted a vhd to vhdx and extended the size of vhdx but when I am trying to extend the size of the partition under Virtual Machines Diskmgmt, the extend volume option is grayed out but the unallocated space is there and when I right click on the unallocated space, all the options are grayed out.

Any Suggestions.

Both Hyper-v and Virtual Server are Windows 2012 R2 Data Center.

Thanks.

I noticed that the partition I need to extend is MBR. How can I convert it to GPT as the option to convert to GPT is also grayed out.