"Response received is incomplete" - vb.net

Question

So I reversed the syntax of this send sms code from c# to vb net so I can reuse it.
The code works sometimes, but for some reason it would often give me the "response received is incomplete" exception.
I was thinking perhaps my code is processing commands faster than my GSM device, could handle, so I tried increasing the timeout response for the serial port, still ends up with this exception.
What do you think is the problem and what would you recommend I do to solve it?
Public Class SmsHelper
Public receiveNow As AutoResetEvent
#Region "Open and Close Ports"
'Open Port
Public Function OpenPort(portName As String, baudRate As Integer, dataBits As Integer, readTimeout As Integer, writeTimeout As Integer) As SerialPort
receiveNow = New AutoResetEvent(False)
Dim port As New SerialPort()
Try
port.PortName = portName
'COM1
port.BaudRate = baudRate
'9600
port.DataBits = dataBits
'8
port.StopBits = StopBits.One
'1
port.Parity = Parity.None
'None
port.ReadTimeout = readTimeout
'300
port.WriteTimeout = writeTimeout
'300
port.Encoding = Encoding.GetEncoding("iso-8859-1")
port.NewLine = vbCrLf
AddHandler port.DataReceived, AddressOf port_DataReceived
port.Open()
port.DtrEnable = True
port.RtsEnable = True
Catch ex As Exception
Throw ex
End Try
Return port
End Function
' Send AT Command
Public Function SendATCommand(port As SerialPort, command As String, responseTimeout As Integer, errorMessage As String) As String
Try
port.DiscardOutBuffer()
port.DiscardInBuffer()
receiveNow.Reset()
port.Write(command & Convert.ToString(vbCrLf))
Dim input As String = ReadResponse(port, responseTimeout)
Console.WriteLine("Received data is " & input)
If (input.Length = 0) OrElse ((Not input.EndsWith(vbCr & vbLf & "> ")) AndAlso (Not input.EndsWith(vbCr & vbLf & "OK" & vbCr & vbLf))) Then
Throw New ApplicationException("No success message was received.")
End If
Return input
Catch ex As Exception
Throw ex
Finally
End Try
End Function
'Receive data from port
Public Sub port_DataReceived(sender As Object, e As SerialDataReceivedEventArgs)
Try
If e.EventType = SerialData.Chars Then
receiveNow.[Set]()
End If
Catch ex As Exception
Throw ex
End Try
End Sub
Public Function ReadResponse(port As SerialPort, timeout As Integer) As String
Dim serialPortData As String = ""
Try
Do
If receiveNow.WaitOne(timeout, False) Then
Dim data As String = port.ReadLine()
serialPortData += data
Else
'Console.WriteLine("SerialPortData data is " & serialPortData)
If serialPortData.Length > 0 Then
Console.WriteLine("SerialPortData is " & serialPortData.ToString)
Throw New ApplicationException("Response received is incomplete.")
Else
Throw New ApplicationException("No data received from phone.")
End If
End If
Loop While Not serialPortData.EndsWith(vbCr & vbLf & "OK" & vbCr & vbLf) AndAlso Not serialPortData.EndsWith(vbCr & vbLf & "> ") AndAlso Not serialPortData.EndsWith(vbCr & vbLf & "ERROR" & vbCr & vbLf)
Catch ex As Exception
Throw ex
End Try
Return serialPortData
End Function
Shared readNow As New AutoResetEvent(False)
Public Function SendMessage(port As SerialPort, phoneNo As String, message As String) As Boolean
Dim isSend As Boolean = False
Try
Dim recievedData As String = SendATCommand(port, "AT", 3000, "No phone connected")
Dim command As String = "AT+CMGF=1" + Char.ConvertFromUtf32(13)
recievedData = SendATCommand(port, command, 3000, "Failed to set message format.")
' AT Command Syntax - http://www.smssolutions.net/tutorials/gsm/sendsmsat/
command = (Convert.ToString("AT+CMGS=""") & phoneNo) + """" + Char.ConvertFromUtf32(13)
recievedData = SendATCommand(port, command, 3000, "Failed to accept phoneNo")
'wait(2)
command = message & Char.ConvertFromUtf32(26)
recievedData = SendATCommand(port, command, 3000, "Failed to send message")
Console.WriteLine("Received data is " & recievedData)
If recievedData.EndsWith(vbCr & vbLf & "OK" & vbCr & vbLf) Then
isSend = True
ElseIf recievedData.Contains("ERROR") Then
isSend = False
End If
Return isSend
Catch ex As Exception
Throw ex
End Try
End Function
Private Shared Sub DataReceived(sender As Object, e As SerialDataReceivedEventArgs)
Try
If e.EventType = SerialData.Chars Then
readNow.[Set]()
End If
Catch ex As Exception
Throw ex
End Try
End Sub
#End Region
End Class