The difference between mysql_fetch_array and $db->fetch_array?

[Attilitus]

I have a script which works perfectly with mysql_fetch_array($result), however, when switching it to $db->fetch_array($result) it does not work. It does not give an error, it simply does not return a result.

Is there something fundamentally different between vbulletin's database class fetch_array and mysql_fetch_array?

(All other database class functions are working just fine... I have query_read within the same function and it works perfectly)