I've had a developer helping me with an issue with pagination. He's traced the problem to the Wiki plugin and asked me to post this on his behalf:
I have been facing issues with the wiki plugin. Two of the important issues I noticed are:
1) Category pages are returning 404 error when you click older posts/entries link (whether using default setup or pagination setup). I turned off all the other plugins, the problem was gone but as I reactivated them one by one, the moment wiki was reactivated the 404 error came up again so its surely wiki plugin. I even reverted back to twenty eleven base theme to check out if it was a template issue, and it wasn't because the 404 error still there.
I am running latest wiki 220.127.116.11 version and wordpress version 3.4.1.
I have been reading similar problems on the wordpress forum for this plugin by other users especially the 404 so please let me know what is the issue and can this be fixed?"