非托管代码调试Visual Studio 2012 ErrorCode CXX0017

I want to debug unmanaged Code in Visual Studio 2012. The unmanaged code is based on VB6. It's possible to step through the code. But the value of many variables coudln't be accessed. I receive the errorcoe CXX0017 by Visual Studio 2012. For example I would like to debug a MSXML variable. I don't have a pdb / symbol files of these variables.I want to debug unmanaged Code in Visual Studio