Modbus Plus comm. with Visual Basic

I'm trying to port a rather old DOS program that communicates to a Modicon PLC through ModBus Plus to Visual Basic on Windows NT, using then CyberLogic "NetLib" drivers (the ones shipped by Modicon). I have ported the declares correctly (I guess), and the program compiles and runs with no errors (at least the parameter passing is OK). The problem is that the functions don't seem to work, and I can't figure out why. The driver is correctly installed (the demos work fine). Has anyone written a Visual basic program that uses the Netlib.dll library?. I'd appreciate any help on the subject.