Blog Page 2 redirects to '285' and shows 404 error

Hi,
I hope one of you can help, as I have no idea where else to look. I have two blogs (willisonnet.com and Imagesbycw.com/blog), one of them everything works fine. The other one has a problem. Which is: When I have the permalinks set to ‘postname’ or anything else but ‘default’, instead of jumping to page 2, it goes to willisonnet.com/285 and shows a 404 error. I do not know why. Both sites run the same theme, same plugins, in fact imagesbycw has a few more, wp is the same version, htaccess are the same and serverside both urls are only redirected into their own subfolder. Yet, imagesbycw runs with ‘postnames’ and shows the 2nd page, whereas willisonnet.com does not.
I would really like to not use the ‘default’ permalinks, but at this point it seems to be the only solution.
Thanks for any ideas!