Geoff,

>No I can definitely pass the object through. I created a form and saved it as 'hf1.scx'

That's cool.

>On that form I have a commandbutton which has the following code
>

Objects are always passed by reference in any method.function call. Does this work for you?

oDll=CREATEOBJECT('d1.interface')
lcnt=oDll.InterInit(thisform)
RELEASE oDll

DEFINE CLASS Interface AS CUSTOM OLEPUBLIC
 PROCEDURE InterInit
 PARAMETERS pForm as Form

 WITH pForm
  .AddObject('myContainer','Container')  && Add a Container to the form
  .myContainer.height=150
  .myContainer.width=150
  .myContainer.top=1
  .myContainer.left=1
  .myContainer.visible=.T.
 ENDWITH

 RETURN pForm.myContainer
ENDPROC
ENDDEFINE

>
>this adds the container to my form. What I dont understand is why I cannot pass 'THISFORM'

Also, you might simply return the Name of the container to the form with a return "myContainer" and let the form reference it that way. This might help prevent dangling object references.