Hello Julie.

When I call 'DO' form B I have form A.Hide in Form B's load method, but I get an error that says "Object form A is not found". What is it that I am doing wrong?

In a addition to what Caroline has told you, there is an easy way to hide form in the Form B's load. When Form B's Load method is firing, _Screen.ActiveForm is still pointing to Form A. So all you need in Form B's Load to hide Form A, is this:

IF TYPE( '_Screen.ActiveForm.Name' ) = 'C' AND ;
  LOWER( _Screen.ActiveForm.Name ) == LOWER( '< Name of Form A >' )
  _Screen.ActiveForm.Hide()
ENDIF