I get the next massage within the error log files of my WordPress blogs:

[10-Oct-2010 04:37:43] PHP Warning:  PHP Startup: Unable to load dynamic library '/usr/local/lib/php/extensions/no-debug-zts-20060613/pdo.so' - /usr/local/lib/php/extensions/no-debug-zts-20060613/pdo.so: undefined symbol: compiler_globals_id in Unknown on line 0
[10-Oct-2010 04:37:43] PHP Warning:  PHP Startup: Unable to load dynamic library '/usr/local/lib/php/extensions/no-debug-zts-20060613/pdo_sqlite.so' - /usr/local/lib/php/extensions/no-debug-zts-20060613/pdo_sqlite.so: undefined symbol: php_pdo_register_driver in Unknown on line 0

Exactly what does it mean?

The php configuration is damaged or else you erased the php.ini file. Look at your php install, check php.ini, or request your webhost.