How to access a custom dll file

[Paul Phillips]

I am having trouble accessing a custom dll file in VB .net for a web page.

I am using the <DLLImport way of pulling in the dll. My code is this:
<DllImport("C:\WINNT\system32\PRDewPointV1.dll", CharSet:=CharSet.Auto)> _
Public Shared Function PRDewPointV1(ByVal CalcType As Double, ByVal
UnitsType As Double, ByVal PRESSURE As Double, ByVal DEWPOINTINPUT As Double,
ByVal C6PLUSMOLWTINPUT As Double, ByVal ZINPUT As Double, ByVal ARRAYOUTPUT
As Double) As Double
End Function

My error comes when I try to access the function:

VarOut = PRDewPointV1(CalcType, UnitsType, PRESSURE, DEWPOINTINPUT,
C6PLUSMOLWTINPUT, _
ZINPUT, ARRAYOUTPUT)

The error is 'System.NullReferenceException' occurred.
Object reference not set to an instance of an object.

Any suggestions would be greatly appreciated.

Thanks,

paul