[postgis-users] topology exception??

[Brian Hamlin]

after backing up, I built and installed postGIS 1.3.1. I am trying a 
few more queries..
However, almost immediately I ran into

    TopologyException: side location conflict xxx yyyy
   ERROR: GEOS within() threw an error!
   SQL State: XX000

I can reproduce it with a certain point, as in

SELECT count(*) FROM just_ca
WHERE st_within('POINT(-121.552 38.5126)', just_ca.the_geom)

and also

SELECT count(*) FROM just_ca, gectable
WHERE just_ca.city = 'San Francisco'
  AND
   st_within( SetSRID(gectable.geom_pts2,4326),
      SetSRID( just_ca.the_geom,4326) )

TopologyException:... -122.422 37.7728

   ok, so I attempted to add an isValid() constraint to check things,
and yes, it failed..I have about 1200 polys.. how to find the failures, 
and why?

and what is this topology exception?
  thanks in advance
    -Brian