System.invalidcastexception:specified cast is not valid in VB.NET

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VB

Hi,
Error thrown due to the .Field(Of Integer)("columnname"), please refer to the following code:
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DtSetBO = New System.Data.DataSet
MyCommandBO.Fill(DtSetBO)
Dim BOTable As DataTable = DtSetBO.Tables("InvtDetailTbl")

Dim query = From InvtDetailTbl In BOTable.AsEnumerable()
   Where InvtDetailTbl.Field(Of String)("Product Line") <> ""
  Order By InvtDetailTbl.Field(Of String)("MES Product") Ascending,
           InvtDetailTbl.Field(Of Integer)("Received Date Ageing") Descending Select InvtDetailTbl

Dim sortedInvt As DataTable = query.CopyToDataTable()
Dim view As DataView = New DataView(sortedInvt)
Dim sortedInvtQuery = From rowView As DataRowView In view
          Select rowView
DataGridView1.DataSource = sortedInvtQuery.ToList()

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Please advise what should the correct statement for above issue.

What I have tried:

Tried on CInt, .Field(of String), .Field(of double).
Error persist.