VM disk cannot be resized- Failed to extend the disk

Issue:-

-With the vSphere Client, if you edit a VM's settings and then select one of its virtual disks, the option to resize the disk is greyed out.
-When trying to extend the disk using vmkftools for resizing, you will receive the below error:
Failed to extend the disk. Failed to lock the file.
-When you extend the disk using vsphere client, the change is not getting reflected.

Root cause:-

The VM will be having a snapshot. Because when a snaphot is taken the actual VMDK file will be locked and the changes will be written to a new delta file. Due to this reason, the actual VMDK file could not be resized. 

Another possible reason: If the disk is IDE, the change may not get reflected. The resolution step for this issue is mentioned here 

Resolution:-

Remove the snapshot file and then try to resize.