Ever since I upgraded to WordPress 2.3, everytime I posted a new post or a new comment it was showing an error wp_post2cat table does not exist. At first I thought there was some error in upgrading but a simple Google search led me to the WordPress forum where I found the solution.
The problem arises in WordPress 2.3 mainly due to incompatible plugins and themes. Some of the plugins which cause this error in WordPress 2.3 are :
- Google Sitemaps Generator older than 3.0 (Download new version here)
- Posts by Author plugin
- Ultimate Tag Warrior
So if you are getting the same error then try upgrading your plugins. It might solve the problem.
If the problem still exists then you can see this WordPress support thread.