Access Violation at Listview click

I am getting an Access Violation when clicking a ListView component.
The de{*word*81} is stopping at the line:

abc:=Listview.selected.Caption;

where abc is a global string variable set in a different program. This program is used
several times and will be created and destroyed every time when it is called.

How can I approach this access violation problem. Are there helpful compilersettings avialable?

Mathew