function not found in DLL

Specifically, at launching the main program, I get error window:

???The procedure entry point
?function1@RTRTwrapper@@UAEXV$SomeStruct@M@@@Z could not be located in the
DLL RTRT_dll.dll.???

Basically, I have an interface class and a class that implements it built
into a dll. In the example code below DLL_IMPORT_EXPORT is either
_declspec(dllexport) at the DLL project, and _declspec(dllimport) when the
DLL is used by the main project.

Class DLL_IMPORT_EXPORT MyInterface
{
Virtual void function1(int param) = 0;
Virtual void function2(int param) = 0;
};

Class DLL_IMPORT_EXPORT MyClass : public MyInterface
{
Void function1(SomeStruct param)
{
//body. Can be null
}

void function2(SomeStruct param)
{
//body. Can be null
}

};

I ran Dependency Walker and other programs and do see function1() exists in
the DLL.

The link
http://www.codeproject.com/KB/cpp/howto_export_cpp_classes.aspx#CppMatureApproach
Giovanni Dicanion helpfully provided in my other post mentions my situation
but I have yet to see any pitfall I may have missed. What am I doing wrong?

Thanks

Bo