CONSTRAINT problems

I've got a test table in 7.0.3 where I'm implementing a directory
type structure in a RCS type system. I have a check to ensure that
there are no duplicate filenames within for a specific directory
given the revisionid of 0 (means it's the current revision rather
than a historical one).

CREATE TABLE test (
  id int4 primary key,
  name VARCHAR(20),
  revision int4 default 0,
  directoryid int4,
  CONSTRAINT dupename CHECK (NOT EXISTS (SELECT name FROM test as o
WHERE o.name!=name AND revision=0))
);
CREATE
insert into test values (1,'test','0',NULL);
ERROR:  ExecEvalExpr: unknown expression type 108

-Michael
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