System.Unauthor izedAccessExcep tion error

[JDS]

I am getting the following error in my application:

System.Unauthor izedAccessExcep tion was unhandled
Message="Access to the port is denied."
Source="System"
StackTrace:
at System.IO.Ports .InternalResour ces.WinIOError( Int32
errorCode, String str)
at System.IO.Ports .SerialStream.D ispose(Boolean disposing)
at System.IO.Ports .SerialStream.F inalize()

The application uses a form to get (weight) data from an external
device on a USB connection mapped to a serial port. In normal
operation the form may be opened (ShowDialog) and closed several
times.

The sequence of events is as follows:
- device is disconnected whilst communicating (an error occurs then
but is handled in code)
- form closed
- device reconnected (i.e. USB physically plugged back in)
- form reopened and behaves normally (initially)
...
- error occurs (as above) but the timing is random, i.e. sometimes
soon after reconnection, sometimes whilst communicating with form
open, sometimes not; sometimes on first time form opened, sometimes
after several attempts

The form uses System.IO.Ports .SerialPort; the relevant code is as
follows (Try-Catch error handling removed):

'******* Selected form code *********
Public Shared WithEvents mPort As SerialPort
Private Shared m_FormDefInstan ce As frmWeigh

#Region "Form handling"
Public Shared Property DefInstance() As frmWeigh
...
Set(ByVal value As frmWeigh)
m_FormDefInstan ce = value
End Set
End Property

Private Sub frmWeigh_Load(B yVal sender As Object, ByVal e As
System.EventArg s) Handles Me.Load
...
DefInstance = Me
...
OpenPort()
...
End Sub

Private Sub frmWeigh_FormCl osing(ByVal sender As Object, ByVal e
As System.Windows. Forms.FormClosi ngEventArgs) Handles Me.FormClosing
...
If Not IsNothing(mPort ) Then
If mPort.IsOpen Then
mPort.Close()
End If
mPort = Nothing
End If
If Not IsNothing(m_For mDefInstance) Then
m_FormDefInstan ce = Nothing
End If
End Sub
#End Region

#Region "SerialPort "
Private Sub OpenPort()
...
mPort = New SerialPort()
mPort.Open()
mPort.DiscardIn Buffer()
Me.Timer1.Enabl ed = True
Me.Timer1.Start ()
...
End Sub
#End Region

#Region "Timer"
Private Sub Timer1_Tick(ByV al sender As Object, ByVal e As
System.EventArg s) Handles Timer1.Tick
...
'Code to check status and send command to request data
...
End Sub
#End Region

#Region "Data handling"
Private Shared Sub mPort_DataRecei ved(ByVal sender As Object,
ByVal e As System.IO.Ports .SerialDataRece ivedEventArgs) Handles
mPort.DataRecei ved
Try
Dim Buffer As String = mPort.ReadExist ing()
DefInstance.Beg inInvoke(New DisplayData(Add ressOf
Display), New Object() {Buffer})
End Sub

Public Delegate Sub DisplayData(ByV al Buffer As String)

Private Shared Sub Display(ByVal Buffer As String)
...
'Data processing code
...
End Sub
#End Region
'******* End of form code *********

From the calling code on error:
frmWeigh = Nothing
frmWeigh.Dispos e

I have a feeling that it is because I am not destroying objects
correctly but I am not sure exactly what I am missing. Any help
greatly appreciated.

[Steve Floyd]

I'm having exactly the same error. Issue is reproducable if unplug and replug USB cable and stop my application (crash happens during application rundown).

It appears to be a subtle interaction between FTDI's drivers and Microsoft's SerialPort object.

Can you check to see if you are using FTDI device drivers to give you the virtual COM port? Support at FTDIchip.com told me the stuff below. Haven't tried because don't know where to put their code. I suppose I'd have to override the Dispose method for the Serial Port object and do something there.

How did you fix your problem?
vvvvvvvvvvvvvvv vvvvvvvvvvvvvvv vvvvvvvvv
You could use D2XX APIs to check the device presence and if it is not present close the USB handle or reload the device.

Code snippets are given in D2XX programmer's guide.

Please refer following APIs

FT_OpenEx and FT_Relaod. If FT_OpenEx return False you may call FT_Reload and try opening the handle again.

http://www.ftdichip.co m/Documents/ProgramGuides/D2XX_Programmer 's_Guide(FT_000 071).pdf
^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^ ^^^