Hello,
Where are you trying from? vCenter/Web Client? If from vC then try directly from connection to the host it is registered on.
Is the Delete from disk button greyed out? Can you un-register it and then delete the namespace folder and contents via datastore browser?
Check that it is truly powered off and/or not hung by going to its namespace folder via SSH (cd /vmfs/volumes/DatastoreName/VM_Name/) and if there are any files present that indicate that it is powered-on/hung (a .vmx~ &/or .vswp files etc.) then try to kill the VM world or move these files into a temp folder so the machine can be managed. Check if there are any VM processes either way I guess using the steps below or esxtop (press v and see if there is IO from the VM):
https://kb.vmware.com/kb/1014165
Worst case scenario you could forcibly rm the files from the datastore location via SSH.
Bob
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