Error migrating from SQLite3 to PostGreSQL: No operator matches the given name and argument type (s). You might need to add explicit type casts

SELECT 
  ag.user_id, ag.user_des, ag.user_login, ag.user_pwd, ag.act_readers, 
  ag.h_reader, ag.email, ag.phone, ag.workgroup, ag.suspended, ag.accesstype, 
  ag.firekey, cli.tpdoc
FROM agenda ag 
INNER JOIN Cliente cli ON ag.user_id = cli.doc 
WHERE accesstype = 5 
ORDER BY user_des ASC

I used this query in SQLite3 , but when I migrated to PostgreSQL it returns the following error:

"No operator matches the given name and argument type(s). You might need to add explicit type casts."

I do not understand what it means and I already try several things. Can you help me?