Welcome to the Community,
I have also tried to use the command line tool to resize the parent vmdk manually, but I am getting 'access denied' permission errors
You were lucky this didn't work, otherwise you would have lost the data in the snapshot. Never try to resize a virtual disk with snapshots!
To help you solve this issue, please attach the VM's .vmsd file as well as its latest vmware.log to your next reply post.
André