Assign: The source contains no DataRows even though DataTable contains rows

I tried to find a solution on the forum but nothing worked for my case.

I have dataTable1 which contains 18000 rows.
dataTable2 is checking for duplicates. It has two columns: SerialNo and Count.

So, my expression is following:

dataTable2 = (From d In dataTable1.AsEnumerable
Group d By k=d("Serial_Number").toString.Trim Into grp=Group
Where grp.Count > 1
Let ra = New Object(){k,grp.Count}
Select r=dataTable2.Rows.Add(ra)).CopyToDataTable

My problem: Even though I checked whether dataTable1 contain rows, I’m getting same error - Assign: The source contains no DataRows.

Hi @bp777
is it possible to share the excel file please?