Except Function

there are a few possible reasons

  • missmatching datacolumn datatypes
  • untrimmed values

You can analyse mor in details or give a try with an alternate like

(From d in dt1.AsEnumerable
Let c1 = d(0).toString.Trim
Let chk = dt2.AsEnumerable.Any(Function (d2) d2(0).toString.Trim.Equals(c1))
Where not chk
Select r = d).CopyToDataTable

feel free to adapt the 0 to the column name and if needed add more check cols into the match part

Handling empty results:
:ambulance: :sos: [FirstAid] Handling of The source contains no DataRows exception - News / Tutorials - UiPath Community Forum