This is typically due to an exhaustion of virtual SCSI ports available on the virtual SCSI adapter in a VMware virtual machine. Please look at the configuration of the virtual machine (open vCenter, right click the virtual machine and select 'Edit Settings'). How many SCSI adapters do you have listed, and how many disks do you have mounted to that SCSI adapter?
I am willing to bet you do not have enough free SCSI ports on the virtual SCSI controller to mount the LUN clones required to perform the verification. When this is encountered, SnapDrive returns the error you are seeing, rathe than call the VMware API to add a new SCSI controller (yes, there is a bug opened on this).
In the mean time, I would suggest creating a new virtual SCSI device in the virtual machine. To do this, either add a new disk (via vCenter), specifying a different SCSI controller/port (i.e. SCSI 1:0, or a SCSI identifier that is not in use), or offline an existing LUN/VMDK and reconnect it to a different SCSI controller/port (again, SCSI 1:0). Unfortunately, there is no way to add just a SCSI controller to a virtual machine without a disk connected to it.
If you require assistance with this process, please contact NetApp Support, as we have seen this many times and will be happy to assist.