Hello Dean,
Have you taken and deleted any snapshots on this volume? I would start with the following:
1. Verify communications between the host and the storage
2. Create a snapshot and delete it from the volume using snapdrive on the host.
3. Review system logs on host
4. Review storage messages logs
5. Run the reclaimer from the command line and see if you get any other message indicators.
A support case may help get to the bottom of the issues.
Hope this help
John