Missing out on a position due to false HR advice. What should I do? Following up on my previous question (Academic Progression via Promotion vs via Recruitment), where I wanted to apply for an assistant professor position at a university where I am currently a postdoc. The HR advice then was that I cannot do that as an external applicant and that I need to apply for promotion next year. For more background please see my original question. 

Last week I discovered that a couple of the potential candidates for this position are actually postdocs in a similar situation as mine, and already work for the same university. They are going to give presentations to the staff next week (This is how I knew). This implies that the HR advice to me was not accurate or something odd has happened.  I contacted HR for explanation but didn't receive back.

I missed out on this opportunity due to false advice from HR which is not fair. What are my options?
This, and your earlier question, seem to be very localized. I think that you need to handle it locally. Go back to HR with your new evidence and seek new advice. Challenge it if necessary. Go to whomever is responsible for the new position with whatever advice you get from HR along with your new evidence and ask for advice there. If it is at all unfavorable, ask for an exception. 

It is possible that there is nothing more than a lack of communication or a misinterpretation of rules. But you won't get out of your trap without bringing it to everyone's attention. 

Perhaps you will just learn how the other cases are not the same as yours. But perhaps you can get the gears unstuck with a bit of jiggling.