change
DataRowView row = (DataRowView)this.cblMinistries[i];
to
DataRowView row = (DataRowView)this.cblMinistries.Items[i];
And also in next line you are check the value member of the item with
dr["FormattedMembershipid"]
but you are not selecting such column in your select statement. since you have used this column value in where condition you can directly check as below
if (row["ValueMembercolumnName"].ToString() == this.txtMembershipid.Text)
{
}