Message >> Value cannot be null. Parameter name: key -- Source(BuildXmlFile) >> mscorlib -- StackTrace >> at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add) at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer) at QuotesSayings.BuildXmlFile(String Sort, Boolean IsFromButton) in M:\WORK\OldIspace1\ispace1Latest\Footer\Quotes-Sayings.aspx.cs:line 162