Can't post tweet on my iPad Mini!

Hi. When using the Twitter app, I can't post a tweet.

I get an error message saying

"Saved as draft. Error posting your message. There was an error sending your Tweet. It has been saved as a draft, please try resending later. (Error: forbidden)"

Here's a picture if you want to see that rather then the text: http://i.imgur.com/svvCzHg.jpg

This also happens when I tweet in the mobile site in Safari.

What's really weird is that I can tweet perfectly with my second and third account (I have 3 accounts), but with my main account, I can't tweet! That shows that it's something wrong with my main account, I guess...

What should I do??

I've tried this:

* Rebooting (turning on and of) my iPad the normal way.

* Rebooting (turning on and of) my iPad with holding down HOME + POWER for about 10 seconds.

* Reinstalling Twitter.

* Removing all my Twitter account from the Settings app and putting them back in.

* Contacting Twitter support (no answer...yet)

Please help me!