I get error for CodeClass.ProjectItem. "A namespace may exist in multiple projects so it is not possible to retrieve the name through the ProjectItem"

In my visual studio 2010 plugin, I get error

"A namespace may exist in multiple projects so it is not possible to retrieve the name through the ProjectItem" when i try to execute code "viewModelClass.ProjectItem". Here,viewModelClass is instance of CodeClass. Actualy this viewModelClass is a member of referenced project.

Actually I am try to execute this plugin on a project which has reference of other projects in a same solution. So, solution has three projects, one is main and others are class library projects.

So, i think it gives error when i try to access CodeClass in referenced project.

I dont know how to deal with this error. Does any one have idea?