Entering admin with PHP5 under Apache 2

In addition to the other known answers available in the docs and the FAQ :

It is necessary to modify a parameter in the configuration of the file php.ini

It is the parameter " register_long_arrays " which by default (in PHP5) is set to " Off ". It is enough to set it to " ON " and all functions (access to the administration, recognition at the time of the access to the site).

Here are comments associated with this parameter in the standard file php.ini :

Whether or not to register the old-style input arrays, HTTP_GET_VARS
; and friends. If you're not using them, it's recommended to turn them off,
; for performance reasons.
register_long_arrays = on