DHP apparently means "Designated High Profile" and would appear to require a call to a supervisor before you are allowed to board. I'd do two things:
1. Avoid AC until this is resolved.
2. Get in touch with AC - not sure who and ask that this be resolved ASAP, pointing out that neither UA nor LH have you on any sort of list.

To get some idea of what this can turn in to, see:
http://www.thestar.com/news/world/ar...ith-air-canada

Hopefully it doesn't take you six years to resolve.

Good luck!