I've spent a little time with this and have some more questions. I started by taking your audio demo vi and started to have it call the DLL and am seeing no issues. However, if I run the VB code, I don't get the error you report. I do however see that the hourglass icon is churning away on the program. How do you get the error message you noted before. And do you see this hourslass phenomenon?
Also, I don't use VB very often, but I see that you built your DLL with all your functions set to stdcall (WinAPI). Was this your intent, or should they have been built with the C calling convention?
I haven't finished putting all the DLL calls in the LV version yet, but your problem may be that you are not calling the DLL properly from VB. I'll finish adding the DLL calls in tomorrow to the LV VI and see if I can get any error to generate.