WordPress MU

After upgrading to wpmu 1.2.1, posts, pages and categories links not working on some blogs. Also when I try to post on those blogs, it returns 500 error.
When I try to access posts, pages or categories on those blogs, it gives following warning in the header:

Warning: Invalid argument supplied for foreach() in /home/myusername/public_html/wp-includes/classes.php on line 88

Line 88 of wp-includes/classes.php is this:

foreach ($rewrite as $match => $query) {

What might cause this? Thank you in advance.

Didn't know what was the problem, but it was fixed by creating new pages in each blog.

I had the same problem and found that the problem was caused by invalid data in the rewrite_rules option field of the wp_x_options table

(When I saw this warning, clicking on post titles generated 404 not found errors for that blog)

By restoring this value the problem went away.

Any ideas for a global fix for, say, tens of thousands of blogs :)

Do me a favor and check to see if resaving the permalinks solves the issue. If it does, I think I can work out a fix for you.

Hmmm, having fixed it I need to find some more errors first - I'll get back to you.

And the answer is, yes it does... all I had to do was go into Options>Permalinks and the problem went away.

I strongly suspect it's realted to having non English characters somewhere these have copped up on Japanese and Norwegian edublogs.

Hmm, while you're on that topic, are you switching charsets in MySQL when it comes to blogs with non-english characters?

I too found that all of my links that referred to other pages or individual posts in my blog caused a sort of circular logic error and would fail to a 404 or TRY AGAIN page.

I fixed it (after several hours of searching etc) by

:: downloaded the current version of WordPress

:: went to http://YOUR BLOG NAME/blog/wp-admin/plugins.php page and deactivated all plugins

:: deleted the wp-admin and wp-includes directories in the /blog folder

:: copied the new WordPress files (not the folder, but it's content's) into the /blog directory

:: went to http://YOUR BLOG NAME/blog/wp-admin/ to check for db error messages

:: went to http://YOUR BLOG NAME/blog/wp-admin/plugins.php page and RE-activated all plugins

:: MOST IMPORTANT STEP!!! Went to http://YOUR BLOG NAME/blog/wp-admin/options-permalink.php and made sure DEFAULT is chose under COMMON SETTINGS (mine was set to DAY/TIME) and click SAVE CHANGES

and it worked better than ever!