Thanks for all the suggestions. The problem is finally solved with some help from CJE. It seems there is a bug in some versions of the USDdriver under 5.11. It is essential to have release 3. Steve -- Steve Ellacott, Computing, Mathematical and Information Sciences, University of Brighton, Moulsecoomb, BN2 4GJ, UK Tel: 01273 885845 Office: 01273 642544 Fax: 01273 642405 WWW: http://www.it.brighton.ac.uk/staff/swe