"Items collection cannot be modified when the DataSource property is set."

It looks like it's telling you that you can't do an Items.Add() to lstEmployees when you've set the DataSource on lstEmployees and called DataBind().

Without more code I can't say more.

The error message tells us that you have set the "DataSource property" on "lstEmployees". So go to "lstEmployees" properties and remove the DataSource - or if you want to keep the DataSource, don´t try to add "your own" items to "lstEmployees", as it won´t be accepted.

Once you add a .DataSource to your listbox, you cannot modify the ListBox.Items collection. Instead, you can modify the original source.

For example, if your listbox is bound to a generic list of strings:

List<string> myList = new List<string>();
myList.Add("Item 1");
myList.Add("Item 2");
myList.Add("Item 3");

myListBox.DataSource = myList;

// need to add an item to the list after it's bound
myList.Add("No records found.");