can't move roundcube to another server directory

[com2]

I first tried out the new version in temporal folder, a subfolder of the old version for instance /var/www/rcube/rcubenew.

The new version seems to work all right, so I move it to /var/www/rcubenew , renamed the old one to  /var/www/rcubeold and the new one to /var/www/rcube This operaition I could freely do previous version, but apparently there is something different in 1.02 because it shows me the WSOD now.

What is causing this? How to fix it? I don't see the document root stored anywhere (in config or database).

[com2]

PHP Fatal error:  Class 'html' not found in /var/www/rcube/rcubenew/program/lib/Roundcube/rcube_plugin_api.php on line 564

[com2]

Must be some kind of caching problem (xcache in my case) because when I changed from mod_php to fastcgi, the problem was not reproducible. I don't know if you can do that inside PHP, but may be some cache flushing should be included to prevent this?