Try each of the following steps in order until the error is resolved:

1. Exit and sign out, then log back in and and post again

2. Check the security settings for the user to ensure they have the rights to post.  Give the user security rights if necessary  [Version 7]  

3. Post from another workstation, logged in as the same user name. If this is successful, uninstall and reinstall the problematic workstation  [Version 7]

4. Log in as Supervisor and post. If this is successful, create a new user name  [Version 7]