mysql_real_escape_string vs. mysql_escape_string

[wmhop]

Using the following line of code will set $first_name to the value of $_SESSION['first_name']);

$first_name = mysql_escape_string($_SESSION['first_name']);

but using

$first_name = mysql_real_escape_string($_SESSION['first_name']);

seems to replace the value with an empty string

does anyone know what would cause this problem.

mysql 4.1.12
php 5.0.5

one additional note: my web host has the same version of mysql and php but the mysql_real_escape_string code works on their servers they're using unix I'm on windows xp