The most common cause of a blank screen at any stage in the process, if your source view shows empty, is that PHP aborted during its run without dumping buffers. During software upgrades, this is usually due to one of three reasons:
- An incomplete transfer of the requisite files. Don’t insist that you’re certain that didn’t happen, even if it’s from a command like svn or cp that shouldn’t fail; you’re not certain until you’ve checked.
- PHP has run out of some resource, typically RAM.
- mod_security is set up brokenly
[digg-reddit-me]In both cases, you can figure out which by checking your apache logs. On windows, go to the Windows Event Viewer. On unix, this may live in a variety of places; most common is shared hosting by cpanel/plesk, where you can get it in your control panel, or to just look in /var/logs/ .
If it’s #1, you’re likely to see something like this in logs (this is from my site, which just suffered this problem and was quickly fixed) :
[Tue Jul 15 18:45:28 2008] [error] [client 24.117...] PHP Fatal error: Call to undefined function force_ssl_admin() in /var/www/html/wp-settings.php on line 390, referer: http://.../wp-admin/post.php?action=edit&post=55
Don’t worry if that undefined function has a different name or a different referrer, or whatever; that’s how you track down missing code, and missing code means some file didn’t get updated.