Conflict between EnvDTE dlls

Question

I have an Addin to visual studio that adds a configuration option to the user project when the user clicks on right menu click, and does something when he runs his project:

public void OnConnection(object application, ext_ConnectMode connectMode, object addInInst, ref Array custom)
{
    _applicationObject = (DTE2)application;
    _addInInstance = (AddIn)addInInst;

    events = _applicationObject.Events;
    dbgEvents = events.DebuggerEvents;

    if (!registered)
    {
        dbgEvents.OnEnterRunMode += new _dispDebuggerEvents_OnEnterRunModeEventHandler(DebuggerEvents_OnEnterRunMode);
        registered = true;
    }
    if ((connectMode == ext_ConnectMode.ext_cm_AfterStartup))
    {
        //add right click menu
    }
}
//...
//when click on the right click menu
public void Exec(string commandName, vsCommandExecOption executeOption, ref object varIn, ref object varOut, ref bool handled)
{
    handled = false;
    if (executeOption == vsCommandExecOption.vsCommandExecOptionDoDefault)
    {
        if (commandName == _addInInstance.ProgID + "." + PROJECT_COMMAND_NAME)
        {
            //...
            //add configuration option
            Solution2 sol = (Solution2)_applicationObject.Solution;
            var pro = sol.Projects.Item(1).Object;
            var tool = pro.Configurations.item(ConfigName).Tools("VCCLCompilerTool");
            //...

            handled = true;
            return;
        }
    }
}

...

void DebuggerEvents_OnEnterRunMode(dbgEventReason Reason)
{
    if (Reason == dbgEventReason.dbgEventReasonLaunchProgram || (Reason == dbgEventReason.dbgEventReasonGo && isLunchProgram))
    {
        //do something
    }
}

private EnvDTE.Events events;
private EnvDTE.DebuggerEvents dbgEvents;
//...
private AddIn _addInInstance;
private OutputWindowPane _outpuWindow;

The Configurations property in pro.Configurations exists in:

C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\PublicAssemblies\EnvDTE.dll

but when there is reference to it, the DebuggerEvents_OnEnterRunMode() event doesn't fire. I replaced this reference with

c:\Windows\assembly\GAC\EnvDTE\8.0.0.0__b03f5f7f11d50a3a\envdte.dll

and now the event called, but the Configurations property is undefined. So I added both.

In order to avoid conflict between the same namespace, according the instructions in two different DLL with same namespace and in aliases, I define the Alias property of

c:\Windows\assembly\GAC\EnvDTE\8.0.0.0__b03f5f7f11d50a3a\envdte.dll

as X, and add the line extern alias X;, but the problem is that when I try to write

var tool = pro.X::EnvDTE.Configurations.item(ConfigName).Tools("VCCLCompilerTool");

or

var tool = pro.(X::EnvDTE.Configurations).item(ConfigName).Tools("VCCLCompilerTool");

I get a compile error:

object does not contain a definition for 'X' and no extension method 'X' accepting a first argument of type 'object' could be found (are you missing a using directive or an assembly reference?).

what should I do?