Could you please give more information? What kind of system are you working with? Do you have an embedded controller or are you connecting to a VXI chassis via MXI-2, MXI-3, USB, or 1394? Do you have an error code in particular? Is it a LabVIEW application or a text based program? If you are using LabVIEW, what version? What versions of NI-VISA and NI-VXI do you have? Is the title of this question the exact error you are seeing? If not, could you post the entire error? The more specific your question the better able we'll be to help find a solution.