Here’s a possible solution.
If you use the Bad Behavior plugin (which Miraz and I recommend), you may have found that you suddenly cannot post to your blog. In fact, you can’t make any changes at all.
Don’t panic. Download and install the updated Bad Behavior Plugin, version 2.0.11. You can get it here:
http://www.bad-behavior.ioerror.us/2007/12/06/bad-behavior-2011/.
The above URL also provides information on why this problem occurs.