How to create a ParseError object

I have created a class that inherit from CSharpParser and overwritten the Parse method so I can add compiler errors. See code below:

public class myParser : CSharpParser {
        public myParser (CSharpGrammar grm, string key ) : base(grm) {

        }
        public override IParseData Parse(IParseRequest request) {
            IParseData res = base.Parse(request);
            IDotNetParseData tmp = res as IDotNetParseData;
            System.Collections.Generic.List<IParseError> lst = tmp.Errors as System.Collections.Generic.List<IParseError>;
            // How to add errors 

            return res;
        }

    }

I can add items to the List<IParseError> lst, but how do I create errors?