I'm assuming since you're using VB 3, I assume you're calling directly into gpib-32.dll - is that correct? Could you possibly post the VB code? Also, if it's possible for you to use a later version of VB, we have ActiveX controls for VB6 and .NET classes for VB.NET that would make GPIB-based I/O much simpler to do than it would be in VB 3.0