mysql-unknown-column-in-on-clause

When i have made a left join, i got an error :
mysql-unknown-column-in-on-clause

The solution was to place parenthese into link join.

For more information :
http://stackoverflow.com/questions/10483421/mysql-unknown-column-in-on-clause

example : 
left join block_weather_station bws on (bws.block_id = b.block_id) ...
=> WORK

left join block_weather_station bws on bws.block_id = b.block_id ...
=> DOESN'T WORK