Not able to remove a software

Error Number: 0x80040703
Description:Failed to find dll function: SAM.AddProperty

I am able to load the dll but not call the methods.

The method that is being called from my c++.NET dll is:
void AddProperty(String *name, String *value) throw(...);

Below is my install script:

prototype SAM.AddProperty(POINTER,POINTER);
nResult = UseDLL(SUPPORTDIR ^ "SAM.dll");

STRING sKey;
STRING sValue;
POINTER psKey;
POINTER psValue;
sKey="Key";
sValue="Value";

psKey = &sKey;
psValue=&sValue;

AddProperty(psKey, psValue);

I also tried sending in STRINGS instead of POINTER but that didn't work either.

prototype SAM.AddProperty(STRING,STRING);
nResult = UseDLL(SUPPORTDIR ^ "SAM.dll");

STRING sKey;
STRING sValue;

sKey="Key";
sValue="Value";

AddProperty(sKey, sValue);