To reset the LUn so it can be presented to the ESX host:

Ensure that no ESX hosts are using or locking the LUN.

In the VI Client, select the ESX host and select the configuration tab
Click on "Advanced Settings"
Select LVM in the left pane
Set LVM.EnableResignature to 1 and click OK
Click "Storage Adapters"
Click "Rescan", then click OK
Click on Storage (SCSI, SAN and NFS)
The volume should now appear as snapshot-xxx
Right click and select "Rename" from the context menu
Click on "Advanced Settings"
Select LVM in the left pane
Set LVM.EnableResignature to 0 and click OK

On the remaining ESX hosts:

Select the ESX host
Select the Configuration tab
Click Storage Adapters
Click Rescan
Click OK
Click on Storage (SCSI, SAN, NFS)
The volume should now appear fine.