... it came back with an error Invalid configuration ...
From my experience this error message is usually caused by invalid entries in the VM's .vmsd file. In most cases this can easily be fixed by deleting the .vmsd file. In order to delete this file, shut down the VM, remove it from the inventory, delete the .vmsd file and then re-add the VM to the inventory. Instead of removing and re-adding the VM you can also reload the VM from the command line (see http://kb.vmware.com/kb/1026043) after deleting the .vmsd file, which - depending on your environment may be the better way to do this.Once done create a new snapshot and run "Delete All".
If you are unsure, please attach the VM's .vmx and .vmsd file to your next reply post and provide a screenshot of the datastore browser window showing all the VM's files (with sizes, time stamps, ...)
André