I could be a Real smart-ass and suggest putting in a bid at 0.001...but I'm not like that. But I bet it would go through!
Seriously, it sounds like you may have to call your broker directly and get them to look at the account to determine if there is a problem. OR tell you something that you are doing wrong. By what you describe, either 0.0005 or 0.0006 should work without issue.