MPF: project properties -> "Visual Studio has encountered an unexpected error."

Hello,

I am trying to implement a VisualStudio project type. Currently, I can load a project and can add several individual leafs/nodes. Anyway, when I try to open the project's properties I am getting the error message "Visual Studio has encountered an unexpected error."

The only modifications I did are:

public class TcHmiProjectNode : ProjectNode
    {
        private TcHmiPackagePackage package;

        public TcHmiProjectNode(TcHmiPackagePackage package)
        {
            this.package = package;
            this.package.TcHmiProjectNode = this;
        }

        public override Guid ProjectGuid
        {
            get { return typeof(TcHmiProjectFactory).GUID; }
        }

        public override string ProjectType
        {
            get { return "TcHmiProject"; }
        }

        public override void AddFileFromTemplate(string source, string target)
        {
            this.FileTemplateProcessor.UntokenFile(source, target);
            this.FileTemplateProcessor.Reset();
        }
    }