Könnte am
safe_mode von PHP liegen.
Beim safe_mode erlaubt PHP exec & Co. nur in einem bestimmten Verzeichnis und/oder bestimmte Funktionen können abgeschaltet werden.
Auszug aus der php.ini:
When safe_mode is on, only executables located in the safe_mode_exec_dir
; will be allowed to be executed via the exec family of functions.
safe_mode_exec_dir =
; This directive allows you to disable certain functions for security reasons.
; It receives a comma-delimited list of function names. This directive is
; *NOT* affected by whether Safe Mode is turned On or Off.
disable_functions =
; open_basedir, if set, limits all file operations to the defined directory
; and below. This directive makes most sense if used in a per-directory
; or per-virtualhost web server configuration file. This directive is
; *NOT* affected by whether Safe Mode is turned On or Off.
open_basedir =