Rails - Jan 2005 - sql update string length error

I''m receiving errors when I attempt to save records back into the
database.  Apparently there may be some limitation on the string
length passed to the database for updating.  The error message in the
log file looks like this:

ActiveRecord::StatementInvalid (ERROR:  value too long for type
character varying(256) : UPDATE ...

The update string that''s causing this errors works fine when entering
directly into the database console.
I''m using Rails 0.9.3 and the db adapter for PostgreSQL(version 7.4.6).
Any ideas why this is happening?

Thanks,
Robbie