A first chance exception of type 'System.IO.FileNotFoundException' occurred in mscorlib.dll

I have a vb.net code which reads from a text file all network locations and then calculated the MD5 hash of those files and then further write hash values to output.txt file ... Program stops working after 500 lines and throw following error ... following is the code and error messages

CODE:

        Dim sNames As String() = {"A"}


        System.Threading.Tasks.Parallel.For(0, sNames.Count, Sub(i)

                                                                 For Each line As String In lines
                                                                     file.Write(MD5(line, 2))
                                                                     file.Write("@")
                                                                     file.WriteLine(line)
                                                                     ' i += 1

                                                                     ProgressBar1.Value += 1

                                                                 Next
                                                             End Sub)




        file.Close()

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ERRORS:

A first chance exception of type 'System.IO.FileNotFoundException' occurred in mscorlib.dll
A first chance exception of type 'System.ArgumentException' occurred in mscorlib.dll
A first chance exception of type 'System.IO.FileNotFoundException' occurred in mscorlib.dll
A first chance exception of type 'System.IO.FileNotFoundException' occurred in mscorlib.dll
A first chance exception of type 'System.ArgumentException' occurred in mscorlib.dll
A first chance exception of type 'System.IO.FileNotFoundException' occurred in mscorlib.dll
A first chance exception of type 'System.IO.FileNotFoundException' occurred in mscorlib.dll
A first chance exception of type 'System.IO.FileNotFoundException' occurred in mscorlib.dll
A first chance exception of type 'System.IO.FileNotFoundException' occurred in mscorlib.dll
A first chance exception of type 'System.IO.FileNotFoundException' occurred in mscorlib.dll
A first chance exception of type 'System.ArgumentException' occurred in mscorlib.dll
The program '[11208] WindowsApplication1.vshost.exe' has exited with code 0 (0x0).

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