extractValue and right outer join - Oracle SQL

[prim3geek]

i got a little (at least i hope so) problem with an SQL Query. Here's my join\[code\]WHERE obj.mod_type = 'SER' and obj.wrk_id=wrk_lang.id(+) and extractvalue(value(shm),'/*/@xmi:id','xmlns:xmi="http://www.omg.org/XMI"') = extractvalue(value(shm_con),'/*/@source')(+)\[/code\]It gives me an "ORA-00936: missing expression"When i remove the second outer join it works fine(also with a regular join).Can smb. help me?