Take a look at this :

To: "Steve Williams" <s.r.williams@...>
From: "Petr Vones" <petr_v@...>
Subject: Re: TComboBox Empty String Error Delphi7
Date: Tue, 24 Sep 2002 22:42:54 +0200
Groups: borland.public.delphi.vcl.components.using

TComboBox patch for Delphi 7 (QC #2246)
http://codecentral.borland.com/codecentral/ccWeb.exe/listing?id=18872

Problem: Selecting an empty string in TComboBox component will cause Access
Violation on some systems. See details in Quality Central report #2246.

Description: On some systems (Windows 2000 SP3) it will cause Access Violation
in ntdll.dll because the code in TCustomComboBoxStrings.Get method passes nil
to the API function call for an empty string item.

The patch fixes it for both standalone executables or applications compiled
with runtime packages. To use it just add D7ComboBoxStringsGetPatch.pas unit
to the project.

Note: It will not work if the application is compiled with Debug DCUs

--
Petr Vones