1. Create a dummy/test snapshot and uncheck the option to include cpu & memory in the snapshot. (it will create a very small snapshot)
2. Then do a delete all now in the snapshot manager and that works
OR
if the above didnt work then
1. storage vmotion the VM to another lun/datastore and it is the easiest of all.
OR
1. clone the VM
OR
if there is no space for cloning or sVmotion then try consolidating snapshots through the command line.
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