Consider the following query (heavily reduced and thus rendered meaningless)...
from Users user0_,
left outer join Users user3_ on forum1_.Manager = user3_.Id
If you will try to run it, it will fail, complaining:
The multi-part identifier "forum1_.Manager" could not be bound.
This is even though this should work. I run the same query on MySQL, and it passed cleanly (although this is not saying anything, of course :-) ). I currently don't have a handy Oracle box to test this, so I have to rely on just those two data points. It works on MySQL, fails in MS SQL.
The issues seems to be the orderring in the from clause. If I replace Forum and Messages, it works, but I am not sure why.