PHP Warning: Xdebug MUST be loaded as a Zend extension

Just switch extension to zend_extension in your active php.ini file.

For anyone else who is having this issue, I updated this in my php.ini file and it fixed the error:

; Directory in which the loadable extensions (modules) reside.
extension_dir = "/usr/local/lib/php/extensions/no-debug-non-zts-20090626"
zend_extension = "/usr/local/IonCube/ioncube_loader_lin_5.3.so"
zend_extension = "/usr/local/lib/php/extensions/no-debug-non-zts-20090626/xdebug.so"
extension = "pdo.so"
extension = "pdo_sqlite.so"
extension = "pdo_mysql.so"
extension = "sqlite.so"