Sadviser – My 4.0 install left me with quite a few blog posts that are now WSOD on the front end. Most posts are o.k. even on the front end. After asking around, I suspect my Thesis Theme which is at the highest rev. level prior to the introduction of 2.0.
If you have are using a theme, you might want to delete your theme before you convert from 3.9.2 to 4.0+. Then select a theme that is “supported”.
