setlocale returns FALSE sometimes

Hi list,


I have a few locales installed on my system:

locale -a
C
POSIX
dutch
nl_BE
nl_BE.iso88591
nl_BE.iso885915@euro
nl_BE.utf8
nl_BE.utf8@euro
nl_BE@euro
nl_NL
nl_NL.iso88591
nl_NL.iso885915@euro
nl_NL.utf8
nl_NL.utf8@euro
nl_NL@euro


In my PHP code I have the following two lines:

if( !setlocale(LC_TIME, 'nl_NL') ) {
    die("Failed setting locale");
}


Now when I load this script a few times, sometimes I get the message "Failed 
setting locale", but not every time.

Why does this happen or what can I do to overcome this?