Passing vb.net object byref to unmanaged code

Question

I am rasing an event from managed vb.net code which is being handled in unmanaged vc++ code. Below is the code line :

Dim pCALMarkups as Object
RaiseEvent RequestEISData(nOrdinal, pCALMarkups, eMarkupCreateSecurity, eMarkupModifySecurity, eMarkupDeleteSecurity, sUserNameSecurity)

pCALMarkups object is being passed as reference and will be initialized in unmanaged vc++ code. Below is the declaration of the event in VB.NET:

 Public Event RequestEISData(ByVal nOrdinal As Short, <[In](), [Out]()> <MarshalAs(UnmanagedType.IDispatch)> ByRef pCALMarkups As Object, ByRef eMarkupCreateSecurity As Short, ByRef eMarkupModifySecurity As Short, ByRef eMarkupDeleteSecurity As Short, ByRef sUserNameSecurity As String)

Below is the function which is handling this event in VC++

 void __stdcall OnRequestEISDataViewer(short nOrdinal, 
                                     IDispatch **pMarkups, 
                                     short *eMarkupCreateSecurity,
                                     short *eMarkupModifySecurity,
                                     short *eMarkupDeleteSecurity,
                                     BSTR *sUserNameSecurity)
{  CCALPageMarkups* pCalMarkups = new CComObject <CCALPageMarkups>;
   // CCALPageMarkups is a class declared in vc++ code
   // Some code for initializing pCalMarkups 
  *pMarkups = pCalMarkups;  //last line of code in this function 
}

During debugging of the code I am able to step into the OnRequestEISDataViewer function , everything inside that function is being executed without any error, but when control comes out of the function after executing last line it is showing the below mentioned error :

"Managed Debugging Assistant 'InvalidVariant' has detected a problem in 'D:\Shared Folder\Workman code\UI\bin\WorkMan.exe'. Additional Information: An invalid VARIANT was detected during a conversion from an unmanaged VARIANT to a managed object. Passing invalid VARIANTs to the CLR can cause unexpected exceptions, corruption or data loss"

So how do I strong type or Marshal pCALMarups object in VB.NET code so that this error will be resolved ? or Do I have to change vc++ code ? Any suggestion is appreciated.