If you recently upgraded to wordpress 2.6 and noticed that all your categories just went blank (missing), you are in lil trouble. I recently upgraded a blog to  wordpress 2.6 from a older version of wordpress and all my categories went blank. I was in more trouble as i did not do a backup of my wordpress database.

If you have made a backup of wordpress database you can follow the Article written by David Cumps to fix the missing categories for wordpress 2.6. If you havent, its a lesson which you should learn “Always Back up your Database”

How to recover my categories when i dont have a SQL backup?

Note: This method works only if you blog dates back to February 2008 (6 months back from the present)

It is not easy to recover the Categories 100% if you do not know your blog well. Head straight to web.archive.org (it does not keep recent archives) and have a look at the categories there and the posts in those categories for your blog. Head to the categories manage page of your blog where the names are missing and you can see the number of Posts. Click on the number and you can see the posts there. Compare it to Wayback machine. If you find the posts match get the category id from the linkbar and then
http://your-site/wp-admin/categories.php?action=edit&cat_ID=<cat id>
hit the above link replacing it with your site name and the category and Edit it to the name you matched from Wayback machine.

It’s a very tidious process and you can recover your categories only if your blog is old enough and you know your blog well as in the categories you had added in your blog.

Wordpress 2.6.1 is released. Im writing this just to help out people who have made the mistake of not backing up your database.