After upgrading from SME 6.0 to SME 7.0 the webmail stopped working. Pointing the browser to the webmail directory only displays an empty (blank) page, when I were expecting the login page. There is no error message in the browser. How can I troubleshoot this, is there some log files that could be checked for error messages? I have already verified that I have the correct horde, imp and turba rpms. Does the webmail require special php settings?