HI Terry Many thanks for your most helpful and comprehensive response.  Much appreciated.  In fact your message, and in particular 'take ownership' got me thinking and remembered that I had encountered this before. The solution proved quite simple and indeed worked just fine in my present case.  In the previous case the issue arose when I moved a hard disc to a different computer.  So I recalled that I had also moved the discs that contains my driverpool to a different machine tha