Horde webmail stops working after installation of Zend Optimizer or manual PHP installation

After installation of Zend Optimizer or manual PHP installation Horde webmail stops to work.

The following error is displayed when trying to browse webmail website:

Warning: main(PEAR.php): failed to open stream: No such file or directory in C:Inetpubvhostswebmailhordelibcore.php on line 26

Warning: main(): Failed opening 'PEAR.php' for inclusion (include_path='C:Inetpubvhostswebmailhordelib;.;./includes;./pear') in C:Inetpubvhostswebmailhordelibcore.php on line 26

Warning: main(Log.php): failed to open stream: No such file or directory in C:InetpubvhostswebmailhordelibHorde.php on line 3

Warning: main(): Failed opening 'Log.php' for inclusion (include_path='C:Inetpubvhostswebmailhordelib;.;./includes;./pear') in C:InetpubvhostswebmailhordelibHorde.php on line 3

Warning: _connect(DB.php): failed to open stream: No such file or directory in C:InetpubvhostswebmailhordelibHordeDataTreesql.php on line 1255

Fatal error: _connect(): Failed opening required 'DB.php' (include_path='C:Inetpubvhostswebmailhordelib;.;./includes;./pear') in C:InetpubvhostswebmailhordelibHordeDataTreesql.php on line 1255

Cause

PHP and Zend installers force PHP to use a default configuration file for all applications, but horde uses a special configuration file which is placed to its folder.

Resolution

Please open regedit and clean up the default configuration location by removing the following key:

on x86 servers - HKEY_LOCAL_MACHINESOFTWAREphpIniFilePath
on x64 servers - HKEY_LOCAL_MACHINESOFTWAREWow6432NodePHPIniFilePath