How to reslove IndexOutofRange in C# 4.5 framework

I have used a checkedlistbox which contains 5 elements and I want to display such a element that have been checked by the user at runtime, so When I checked 3rd element from out of 5 the checkedlistbox it will through a exception called IndexOutofRange. but the element which is checked (selected ) by me that exists at index no 3 then why it will be happen and how to resolve such unwanted exception?
So please help me whereas I will continued my work and improve my skills and logic too.