Oracle9i Enterprise Edition Release - 64bit, UNIX server

I am running a fairly complex piece of SQL involving several views and keep getting an ORA-00604: error occurred at recursive SQL level 1 together with an "ORA-00904: invalid identifier". The column referenced by the second error does exist.

I've managed to get it working by changing some of the views to inline SQL views, but that's not really a very satisfactory solution. Has anyone come across a similar problem before ?