I recently upgraded MySQL to 5.1.41. Before the upgrade the following SQL worked (or at least I thought I remembered it working...it has been a few weeks since designing this...). Now the SQL gives me an error stating that the "archived" column is ambiguous. How can I write this differently, or is there a different problem I'm not aware of?

I simply want to return the "unit_id", "lease_count" (stored in another table with a unit_id that should correspond with the "a.unit_id"), and "lease_archived_count (stored in another table with a unit_id that should correspond with the "a.unit_id").

SELECT a.unit_id, 
    (SELECT count(*) FROM o_leases WHERE unit_id = a.unit_id AND archived = 0) as lease_count, 
    (SELECT count(*) FROM o_leases WHERE unit_id = a.unit_id AND archived = 1) as lease_archive_count

FROM p_unit a, properties b, portfolio c 

WHERE a.property_id = b.properties_id 
AND b.portfolio_id = c.portfolio_id 
AND a.archived = 0 

Thanks for your help.