Error: File it is being used by another process, even if closed and disposed

Question

I'm having problems to access a file.

Every 1 second (more or less) my application is calling this procedure to download a sourcecodepage and save it in a textfile, the problem is sometimes when is called too much for example more than 50 times I get the error:

"Can't access file, file it is being used by another process"

I've tried to close it and dispose it, but nothing.

EDIT: The file who is causing the error is "OutPutFile" Variable which is a file in %TEMP% dir.

' Get URL SourceCode
Function Get_URL_SourceCode(ByVal url As String, Optional ByVal OutputFile As String = Nothing, Optional ByVal delimit As Boolean = False) As String

    Dim SourceCode As String = String.Empty

    If Want_to_cancel_thread Then Return Nothing

    Try
        Dim request As HttpWebRequest = HttpWebRequest.Create(url)
        Dim response As HttpWebResponse = request.GetResponse()
        Dim sr As StreamReader = New StreamReader(response.GetResponseStream())
        SourceCode = sr.ReadToEnd()
        sr.Close() : sr.Dispose()

        If delimit Then SourceCode = Delimit_String(SourceCode, "<div id=""centercol"">", "<!--/centercol -->")

        If OutputFile IsNot Nothing Then

            'File.Open(OutputFile, FileMode.CreateNew, FileAccess.Write, FileShare.Write)
            'Using TextFile As New StreamWriter(OutputFile, False, Encoding.Default)
            '    TextFile.WriteLine(SourceCode)
            'End Using
            File.WriteAllText(OutputFile, SourceCode, Encoding.Default)
        End If

    Catch ex As Exception
        MsgBox("Error: " & ex.Message)
    End Try

    Return SourceCode

End Function

Answer 1

Try using SyncLock so the working thread locks the object and no other process access the file:

'Global variable lock

Dim objectLock As Object = New Object


Function Get_URL_SourceCode(ByVal url As String, Optional ByVal OutputFile As String = Nothing, Optional ByVal delimit As Boolean = False) As String

 Dim SourceCode As String = String.Empty

 'Lock object
 SyncLock objectLock 

 If Want_to_cancel_thread Then Return Nothing

    Try
        Dim request As HttpWebRequest = HttpWebRequest.Create(url)
        Dim response As HttpWebResponse = request.GetResponse()
        Dim sr As StreamReader = New StreamReader(response.GetResponseStream())
        SourceCode = sr.ReadToEnd()
        sr.Close() : sr.Dispose()

        If delimit Then SourceCode = Delimit_String(SourceCode, "<div id=""centercol"">", "<!--/centercol -->")

        If OutputFile IsNot Nothing Then

            'File.Open(OutputFile, FileMode.CreateNew, FileAccess.Write, FileShare.Write)
            'Using TextFile As New StreamWriter(OutputFile, False, Encoding.Default)
            '    TextFile.WriteLine(SourceCode)
            'End Using
            File.WriteAllText(OutputFile, SourceCode, Encoding.Default)
        End If

    Catch ex As Exception
        MsgBox("Error: " & ex.Message)
    End Try

    'End lock
    End SyncLock

    Return SourceCode

 End Function