Issue while performing Union on two sequences using Linq

Question

Error: Instance argument cannot convert from System.Collections.Generic.IEnumerable<AnonymousType#1> to System.Linq.IQueryable<AnonymousType#2>. There is a type mismatch between the two sequences I am trying to union. Even after casting the sequences to IEnumerable or IQueryable, I am still unable to perform the union.
Also give that the anonymous types in two sequences match and the null values are handled