LINQ Specified Cast is Not Valid with a ushort Table Column

DECLARE @p4 Int = 0

var one =
    (from ch in TEST_CHARTs
    join a in TEST_CHART_SERIES on ch.CHARTID equals a.CHARTID into a_join
    from cs in a_join.DefaultIfEmpty()
    join ycols in TEST_QUERY_COLS on new { key1 = cs.YAXIS, key2 = ch.QUERYID } equals new { key1 = ycols.COLNAME, key2 = ycols.QUERYID }
    where ch.CHARTID == 1
    select new 
    {
        ch.CHARTID,
        POSITION = 0,
        ycols.QUERYID,
        ycols.Otherblah,
        Blahblahblah = cs.Blahblahblah
    }).ToList();

var two =
    (from ch in TEST_CHARTs
    join xcol in TEST_QUERY_COLS on new { key1 = ch.XAXIS, key2 = ch.QUERYID } equals new { key1 = xcol.COLNAME, key2 = xcol.QUERYID }
    where ch.CHARTID == 1
    select new 
    {
        ch.CHARTID,
        POSITION = 0,
        xcol.QUERYID,
        xcol.Otherblah
    }).ToList();

var three = 
    from x in two
    select new
    {
        x.CHARTID,
        x.POSITION,
        x.QUERYID,
        x.Otherblah,
        Blahblahblah = false
    };

var four = one.Union(three).Distinct();

var projjType = from projT in dtProjList.AsEnumerable()
                where projT.Field<int>("ProjectId") == projId && 
                      projT.Field<int>("FilterId") == 1 
                select projT;