I upgraded to 3.1 from 3.05 today, and I encountered problem after the update. Custom permalinks with %category% did not work properly, they returned 404 errors on all my articles. Simple removing the %category% solved this error, however I’d much prefer keeping it.
I found information from wordpress forum, but much solutions couldnot solve my problem. Actually, there are several people who have reported similar issues and are seeing 500 errors on permalinks and redirects.
Finally, Google was answered. I found the trick. It can solve my worpress problem. Here’s the solution:
Pages Returning 404?s
1. Log in to wp-admin and go to permalinks, click save (this should refresh your permalinks). Check to see if this fixes your permalinks. If not, set to default. 🙂
2. Disable your plugins to remove them out of the equation.
3. Log into your server via sFTP/SSH/FTP and find your .htaccess file. It should be located in the root of your WordPress install.
4. Pull the htaccess file down so that you have a local back up. Once you’ve pulled it down, go ahead and delete it from your server.
5. Go back to wp-admin and visit your permalinks page. try enabling custom permalinks.
6. This should remedy the issue and you can go ahead and reenable your plugins.
Okay, after I followed the instruction. My wodpress blog run well.