Not unique table/alias: 'usertns_group'1066 Please tell me if you spot the error

The code below looks painstakingly long... but pls if u can spot the error, tell me..

I dont see any duplicates of the alias 'usertns_开发者_开发百科group' so i wonder why im getting that error..

post LEFT JOIN category2 as postcategory2 ON( post.category2_id = postcategory2.category2_id )
 LEFT JOIN category1 as category2category1 ON( postcategory2.category1_id = category2category1.category1_id )
 LEFT JOIN tns_group as category1tns_group ON( category2category1.tns_group_id = category1tns_group.tns_group_id ) 
 LEFT JOIN user as postuser ON( post.user_id = postuser.user_id )
 LEFT JOIN tns_group as usertns_group ON( postuser.tns_group_id = usertns_group.tns_group_id )
 LEFT JOIN status as poststatus ON( post.status_id = poststatus.status_id )
 LEFT JOIN tns_group as posttns_group ON( post.tns_group_id = posttns_group.tns_group_id )

thanks..

Maye usertns_group is the name of a column in one of these tables?