mysql_fetch_array error

I am getting this error message with a query, when I know the query is correct. Anybody every come across this?

Warning: mysql_fetch_array(): supplied argument is not a valid MySQL result resource in…

Here is the query:

$car_data_query = mysql_query("SELECT * FROM cars  AS c LEFT JOIN all_car_makes AS acm ON c.make_id=acm.make_id WHERE c.type='u' ORDER BY acm.make_id ASC, c.year DESC");

	while ($car_makes = mysql_fetch_array($car_data_query)){

Any thoughts would be great!

im an idiot

sorry for the post. i had an extension problem. server didnt recognize .inc files