Have you contacted the vendor (I'm assuming that the drivers are from Eagle)? Could it be that the dll could be corrupted? Also, it sounds like the overall architecture is that they have a dll and then CINs that call the dll.. yes?
If so, something else you might want to consider is if you can create LV to replace that C layer and call the dll directly. It might not be too hard if the real reason they did the CINs is because they didn't feel comfortable programming in LV.
Finally, are the drivers online somewhere?
Mike...