How many hosts have this datastore mounted ?
I suspect you tried to delete the file from another host.
Have you tried vmkfstools -u ?
Where is the guest openeerp7 now. Can you check the vmx file and see if the snap is showing in the vmx, or the vmdk file.
If there are no other guests on the datastore. Can you dismount the datastore properly so that you do note get a apd issue the remount it then try t delete the file.
Can you see the file using the datastore browser and delete the file.