I've a SIMILAR problem, and I've produced a patch for IB_Grid.pas. In my situation, the error is rided only if you have TIB_LookupCombo ClearSelection set to true (test it set to false).
You can apply the following patch against IB_Grid.pas, recompile IBO and see (or include the IB_Grid.pas in your project... set a breakpoint in the patch code to be sure you are running the right code, don't compile wiht packages)
(around source line 8240...)

TIB_CustomCombo.CMExit
...(cut)
if ClearSelectionOnExit then
try
ClearSelection( False );
except
on EAbort do
;
end;
Invalidate;
...(cut)

Let me know, since it works good for me and Geoff is testin it too. We would like Jason include in the next subrelease when ready :)
Regards
Marco Menardi

--- In IBObjects@y..., "slsolutions2002" <strtline@a...> wrote:
> Hello:
>
> I have the following:
>
> A form with a TIB_Grid and a TIB_LookupCombo in the grid. In the
> forms OnShow I open 2 queries, one for the TIB_Grid, the other for
> the TIB_LookupCombo. In the forms OnClose I close both queries.
>
> All works fine unless I try to close the form with the
> TIB_LookupCombo in a dropped down state. I then get a "Cannot focus
> a disabled or invisible window". I actually get it twice. If I
> closeup the TIB_LookupCombo before closing the form all works fine.
>
> The error happens when I attempt to close the queries in the forms
> OnClose. Like I said, I get the error twice, once for each query I
> close. I have tried calling the TIB_LookipCombos CloseUp routine
> before closing the queries but the lookup does not close and I still
> get the error.
>
> Thanks