I'm sorry to hear that you have some issues calling cvi functions. There is a shipping example that demonstrates how to call a CVI function and pass a structure. The example can be found in <TestStand>\Examples\StructPassing\C\Struct Passing to a C DLL.seq.
If the example program does not resolve your issues, post again and please describe the problem in detail.
Regards,
Shannon R.
Applications Engineer
National Instruments