"command php5 not in docroot" after upgrade to 10.0.1

[jgauthier]

I just upgraded a system to Plesk Panel 10.0.1, using the official command-line update utility (/usr/local/psa/admin/bin/autoinstaller). There were no errors displayed during the upgrade. The machine is running CentOS 4.2 (i686).

Some of the Apache virtual hosts managed by this system are now showing 500 errors on every PHP page. I checked the error logs for these domains and they showed nothing. I did find something, however, in /etc/httpd/logs/suexec_log:

[2010-12-28 12:02:07]: uid: (10015/xxxxxx) gid: (2523/2523) cmd: php5
[2010-12-28 12:02:07]: command php5 not in docroot (10015)

I have found this fix, but running it and restarting Apache had no effect:

cp -p /usr/local/psa/suexec/psa-suexec /usr/sbin/suexec

How can I resolve this error? I have root access and can run any diagnostics or fixes that are necessary. Thank you in advance for your help.