Tpanel

[[movorack]]

¿Estás desarrollando una aplicación MDI?

Si es el caso:

MDI child forms cannot be put onto a container like a panel, they are
hosted by the MDI client window, which is a special API-level window
that fills the client area of a MDI main form. This is a requirement of
the Windows MDI framework.
You can have additional TWincontrol descendents (like panels or
toolbars) on a MDI main form as long as their Align property is set to
alLeft, alTop, alBottom, or alRight. The MDI client window will adjust
to take up the remaining client area (you can think of it as aligned
with Align = alClient).
If you want a background image under the child forms you can put a
client-aligned TGraphicControl descendent (like TImage) on the main
form. Since TGraphicControls have no window handle they do not
interfere with the MDI child forms and the VCL contains code to draw
the graphic controls onto the MDI client window. Note that this is not
the case in older Delphi versions, though. I don't remember when it was
introduced (D5 or later perhaps). If you use an older version it
requires some code to draw stuff on the MDI client window.

Fuente