datalist days search problem in C#

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C#

C#4.0

Hi all,

Actually I have 4 search bar in search engine location, skills, functional area and industry and this search leads to datalist with some detail with posted date.

now i have to dropdown with 60 days and 30days fresh data filter from that datalist.

so i used this code

 if (ddfreshness.SelectedItem.ToString() == "Any")
        {
            BindDataList();
        }
        else if (ddfreshness.SelectedItem.ToString() == "30 Days")
        {
            foreach (DataListItem dli in DataList1.Items)
            {
//fetching posted date from datalist
                Label l45 = (Label)dli.FindControl("lblprloc2");

                DateTime now = DateTime.Today;
                TimeSpan ts = now - Convert.ToDateTime(l45.Text);
                // Difference in days.

                int differenceInDays = ts.Days;
                string date = Convert.ToString(differenceInDays) + " Days";
               
                if (differenceInDays <= 30)
                {
                   
//bind fuction for the data to same datalist
                    BindDataList();
                    
                }
            }
        }

Collection was modified; enumeration operation may not execute

plz help me for this code.