B4J Question How to catch this error

Sub Application_Error (Error As Exception, StackTrace As String) As Boolean
    Dim TextWriter1 As TextWriter
    TextWriter1.Initialize(File.OpenOutput(File.DirApp, "AppError.log",True))
    Dim er As StringBuilder
    er.Initialize
    Dim dt As String=Mysub.mydate(DateTime.Now, "yyyy-MM-dd HH:mm:ss")
       If srvr.CurrentThreadIndex = 0 Then 'main thread
        LogError(StackTrace)   
        er.Append(dt & " App Error 1: " & Error & CRLF)
        er.Append(Error & CRLF)
        er.Append(StackTrace & CRLF & CRLF & CRLF & CRLF)
        TextWriter1.Write(er.ToString)
        TextWriter1.Close
        Return False
      Else 'handlers threads
        Log(dt & " App Error 2: " & Error)
        er.Append(dt & " App Error 2: " & Error & CRLF)
        er.Append(Error & CRLF)
        er.Append(StackTrace & CRLF & CRLF & CRLF & CRLF)
        TextWriter1.Write(er.ToString)
        TextWriter1.Close
        Return True
       End If
End Sub