If you ship it back to HP they will get you a new barrel free of charge. Lets figure out what is going on before we do that though.
What oil did you use? If you used remoil, or even hoppes light oil, then left it sit in a drawer or something I would not be surprised if you got a little rust. Use CLP or grease or put it in a safe with some sort of humdity control.
Was the cleaning rod brass? If you were using a steel, or a copper washed one, and some of the cheaper ones are, then you could have scratched the finish which lead to rusting. Not sure what HPs are finished in. It is sort of like mellonite or whatever Glock uses but I am not sure.