If you use (or are trying to) the very excellent Roundcube but you keep getting the white screen of death, then here’s something to try.
As a quick test, disable the curl extension in your /etc/php.ini
;extension = curl.so
and restart your webserver…
sudo service httpd restart
If that seems to solve the problem (you can see the login screen and not a whitescreen) then try the fix that worked for me. Move curl.so after imap.so.
Your mileage may vary.