Data modules can only host non-visual controls, and TActiveXControl
is not a non-visual control.
You ask what is the definition of non-visual control. According to this article, the definition is that if the component is derived from TComponent
and not derived from TControl
, then it is a non-visual control.
That said, the inheritance hierarchy for TActiveXControl
is: TObject
, TComObject
, TTypedComObject
, TAutoObject
, TActiveXControl
. So I am at something of a loss at to why it ever appears on your component palette since it is not derived from TComponent
. It would be interesting to know how you registered it. All the same, it's not a non-visual component in the meaning of the act.