BDE error: 13059 (General SQL error)

Hi ,all:
I'm using Windows2000, Delphi 5, BDE 5.11 native Informix
driver to connect to an Informix database.
Connection is ok but when I try to open a table, error happened:
  BDE error: 13059
  Server: -1811
  General SQL error.
  Implicit connection not allowed after an explicit connection.
It happed in my program as well as SQL Explorer and Database Desktop.
Any suggestion? Thanks.