Using double quotes vs single quotes when passing string as a parameter to function

[ping24]

i have a very strange problem, well not really a problem because i've fixed it but still,when i'm trying to connect to mysql db with:\[code\]mysql_connect("server", "user", "pass") or die(mysql_error());\[/code\]im getting:\[quote\] Access denied for user 'user'@'server' (using password: YES)\[/quote\]but when i change the quotes around the password to single quotes:\[code\]mysql_connect("server", "user", 'pass') or die(mysql_error());\[/code\]it works just fine.i dont have this problem in another server i've got.so maybe it's something in the mysql settings or in the php.ini?thanks.