Thank you carlopagliei for the reply; but i am not using the foreach statement. I have a code like ddlTest.DataSource= TestCollection; ddlTest.DataBind(); Otherthan populating the collection from database, i am not manipulating the collection.

I have a piece of code in which collection is assigned to dropdown list's data source property for binding data. When multiple clients access the site simultaniously the following exception was being thrown:"Collection was modified; Enumeration Operation may not execute". Any idea about y this is happening and how to get this code work???