Dim newLines = From line In File.ReadAllLines(path)
               Where Not line.StartsWith("{TAM98}")
File.WriteAllLines(path, newLines)

Dim sb As New System.Text.StringBuilder()
        Dim myFilePath As String = "c:MyFile.txt"
        Dim mySearchToken As String = "{TAM98}"

        For Each line As String In System.IO.File.ReadLines(myFilePath)
            If (String.Compare(Left(line, mySearchToken.Length), mySearchToken, True) <> 0) Then sb.AppendLine(line)
        Next

        System.IO.File.WriteAllText(myFilePath, sb.ToString())