Oracle 8: error meassge 'Capability not supported'.

hi,
I using D3.
I create two types of Users, administrator and the other is non
administrator.
Its working fine for User administrator.
I keep hiting the error when logged in as non admin user.

by looping via below code...Master detail relationship.

TQueryHeader.first ;
while not TQueryHeader.eof do
begin
 try
   Database.StartTransaction ;
    while not TQueryDetail.eof do
    begin
       TQueryDetail.edit ;
       TQueryDetailMyField.value := 'Hello' ;
       TQueryDetail.post ; {error 'Capability not supported' prompted}
       TQueryDetail.next ;
    end ;
  Database.Commit ;
  TQueryHeader.next ;
 except
 ..... Database.rollback ;
end ;

But, if I take out the Database's functions(), that's fine!!! why?
Am i missed out something important?

please help and advise...

thankyou very much,
regards,
Tc