@addy thanks for your reply.  I tried with forName and it's now working.  I had tried this both forName and forPath previously with the same error so I'm not sure why it's working now.  I can't recall what has changed since whilst I was experimenting/diagnosing.  If I experience it again I'll have to take closer notes of the steps I took to reach that step.  Anyhow thanks for your help, it's much appreciated.