{"error": "Missing key, signature and nonce parameters"}

Dim api_key As String = "APIXXXXXXXXXXXXXXXXXX"
Dim api_secret As String = "APIXXXXXXXXXXXXXXXXXX"
Dim client_id As String = "01020304"
Public Function check_balance()
Try
Dim NONCE As String = DateTime.Now.Ticks
Dim SIGNATURE As String = CreateSignature(NONCE)
Dim request As HttpWebRequest
request = DirectCast(WebRequest.Create("https://www.bitstamp.net/api/balance/"), HttpWebRequest)
request.Method = "POST"
request.Headers("key") = api_key
request.Headers("nonce") = NONCE
request.Headers("signature") = SIGNATURE
Dim response As HttpWebResponse = Nothing
Dim reader As StreamReader = Nothing
Dim result As String = Nothing
Try
response = DirectCast(request.GetResponse(), HttpWebResponse)
reader = New StreamReader(response.GetResponseStream())
result = reader.ReadToEnd()
MsgBox(result)
Catch ex As Exception
Return ex.ToString()
Finally
If Not response Is Nothing Then response.Close()
End Try
Return result
Catch ex As Exception
MsgBox(ex.ToString)
End Try
End Function
Private Function CreateSignature(ByVal Nonce As String) As String
Dim msg As String = String.Format("{0}{1}{2}", Nonce, client_id, api_key)
Return ByteArrayToString(SignHMACSHA256(api_secret, StringToByteArray(msg))).ToUpper()
End Function
Private Function SignHMACSHA256(key As [String], data As Byte()) As Byte()
Dim hashMaker As New HMACSHA256(Encoding.ASCII.GetBytes(key))
Return hashMaker.ComputeHash(data)
End Function
Private Function StringToByteArray(str As String) As Byte()
Return System.Text.Encoding.ASCII.GetBytes(str)
End Function
Private Function ByteArrayToString(hash As Byte()) As String
Return BitConverter.ToString(hash).Replace("-", "").ToLower()
End Function