WordPress Comment posting problem

You need to check all of the following options under Dashboard -> Settings -> Discussion:

Before a comment appears

  • Before a comment appears An administrator must always approve the comment
  • Comment author must have a previously approved comment

Comment Moderation

  • Hold a comment in the queue if it contains _ or more links. (A common characteristic of comment spam is a large number of hyperlinks.)
  • When a comment contains any of these words in its content, name, URL, e-mail, or IP, it will be held in the moderation queue. One word or IP per line. It will match inside words, so “press” will match “WordPress”.

Also: do you have any comment-moderation or spam-prevention Plugins active?