@EXEC command not work :(

Hello, PHP is installed in c:\program files\php the PHP script are in network drive \\xxx.xxx.xxx.xxx\scriptdir\ in the PHP script, we try to launch the command @exec(...) with a executable located in c:\program files\ourexecutable\ it's not work :( but if we move the PHP script from \\xxx.xxx.xxx.xxx\scriptdir\ to c:\scriptdir\ then it's work !! everything work good EXCEPT the @EXEC command ... Safe mode in PHP is OFF ... Thanks by advance for you help stephane