WordPress 3.0 RC1 blank page error

Update: Apologies to the author of Hyper Cache, the error isn’t cause by the plug-in. The error is being caused by DB Cache Reloaded. After updating the site to 3.0 final I was getting the error on the update page, disabling DB Cache Reloaded fixed it.

Update 2: DB Cache Reloaded has now been updated and works flawlessly in 3.0, get it here.

I’ve been eagerly awaiting the release of WordPress 3.0 (due any day now!). I plan on making a few changes to my blog once it is released so decided to try out Release Candidate 1 on my development server. At first it all went fine, upgraded the database no problem… then a blank page. Weird! After a couple of page reloads the sparkly new dashboard popped up (it’s not that different, although it does look greyer). Clicking around the admin area I could see this blank page error was randomly occurring on different pages; bugger!

My immediate thought was a plug-in I had installed, as I’m sure this rather large error would have been picked up while testing the WordPress core functionality! Looking at my Apache error log the following error was listed:

[error] [client] PHP Fatal error:  Call to undefined method wpdb::get_blog_prefix() in dev.nooshu.com\\trunk\\httpdocs\\wp-admin\\includes\\user.php on line 260, referer: http://dev.nooshu.com/wp-admin/edit.php?post_type=portfolio

The error is too vague to actually help, but after a little investigating (and from a hunch I had) I disabled any plug-ins involved in page caching; namely DB Cache Reloaded and Hyper Cache. Unfortunately disabling them still didn’t fix the error, so I decided to remove them completely (db-config.ini, advanced-cache.php and db.php removed from the wp-content directory). Suddenly no more blank page errors occurring! Huzzah!

So if you come across the same problem, then check what caching plug-ins you have installed. When 3.0 final is released I’ll be doing a fresh install of both plug-ins. Hopefully that will solve the issue. They are both quite popular plug-ins so I’m sure others have had the same issue.