Thanks for the hint. I had a look at the help-file concerning ptr_first, it mentioned the C_LINK "directory" and the next-pointer, but there are no more entries concerning these items.
Could you please go a bit more into detail on how to handle the next-pointer for Panels?

I coded the following:

...
Testpanel = ptr_first (PanelB);
while (Testpanel != NULL)
{
Testpanel.flags = 0;

Now I'd like to include the statement using the next-pointer.

Thanks a lot!