Base entity interface is IEntity which requires only "object ID {get;set;}" to be implemented. Now, in almost every case ID is of Guid type (except for membership etc). I am using following code to do mapping of interface

...
    AnyPart<IEntity> primaryMap = ReferencesAny(x => x.Primary)
                    .IdentityType<object>() // tried with .IdentityType<Guid>()
                    .EntityIdentifierColumn("PrimaryID")
                    .EntityTypeColumn("PrimaryType")
                    .MetaType<string>();
...

Of course, next I am adding meta values.

So, Now getting error

Source array was not long enough. Check srcIndex and length, and the array's lower bound

And with .IdentityType<Guid>()

could not resolve property: Primary.ID of: Founder.Connection [.SingleOrDefault[Founder.Connection](NHibernate.Linq.NhQueryable`1[Founder.Connection], Quote((x, ) => (OrElse(AndAlso(Equal(x.Primary.ID, 35c2142a-4c17-4b77-96fd-a2570028a211), Equal(x.Secondary.ID, 35c2142a-4c17-4b77-96fd-a2570028a211)), AndAlso(Equal(x.Secondary.ID, 35c2142a-4c17-4b77-96fd-a2570028a211), Equal(x.Primary.ID, 35c2142a-4c17-4b77-96fd-a2570028a211))))), )]

UPDATE:

I tried also with .IdentityType(x=>x.ID) but same problem (Source array was not long enough)

UPDATE II:

Query (Actually whole method containing query) that this error occurs on is bellow:

public IQueryable<Connection> GetConnections(IEntity connectable)
        {
            IQueryable<Connection> query =
                Query().Where(
                    x => x.Primary.ID == connectable.ID || x.Secondary.ID == connectable.ID);
            return query;
        }