I'm sure I'm not the only new member to experience these problems.
When posting, it pops up that one has been posted in the last 360 seconds. Cool, so then I'll wait, and resubmit. Then it says the post has already been submitted (it hasn't).
So then I go back, change it around, add a lot of text, and submit... it STILL says it's already been posted (yet the text is 95% different now).
If this was one time, it would be one thing. But it's happened about 5 separate times, and now I'm just angrily wasting my time.
I think you need to wait the full six minutes before you try post. Log ins count towards the time to. So wait 6 minutes after you log in.