Although I didn’t experience the problem you are describing, it sounds like there are multiple geometries in your table which causes the command to fail. To discover which SRIDs are in your us_states table,
select distinct SRID(the_geom) from us_states;
If there is more than one SRID listed, you need to issue
update us_states set the_geom = setSRID(the_geom, 4269)
Recall that 4269 is the Geographic projection (Lat/Lon) and the datum is NAD83.
If more than one SRID isn’t listed in your table and the SRID displayed is -1, you may see the same behavior as when there are mixed SRIDs in the table. This is just a guess as I have no idea. But if -1 is displayed as the projection of data (meaning the projection is unknown), you can try setting it to 4269 using the aforementioned command to see if this solves your problem.
Hope this helps.
Charity