There have been SEVERAL complaints of odd behavior of Windows 95 many of which have been solved by upgrading to Windows 98.
Barring such a situation. The 1.70 GPIB driver was designed for the newer Windows operating systems (2000/ME).
Try installing the 1.60 driver, if it is not already installed. Don't forget to uninstall the current driver. A similar situation might arise with other drivers installed (DAQ/FieldPoint/etc).
Randy Solomonson
Application Engineer
National Instruments