WP7: Delete IsolatedStorageFile

I would really appreciate some help with deleting a file from IsolatedStorage on WP7. I am basically downloading a file from the web, storing it in Isolated Storage and then uploading it to my Downloads folder in my Dropbox. Once I have uploaded it, I would like to delete the file from Isolated Storage, but am getting Exception errors when trying to do so.

Here is my code :

    public void readCompleteCallback(Object sender, OpenReadCompletedEventArgs e)
    {
        if (e.Error == null)
        {
            try
            {
                //string fileName = txtUrl.Text.Substring(txtUrl.Text.LastIndexOf("/") + 1).Trim();
                string fileName = searchBox.Text + fileExt;
                //string fileName = "DownloadedNZB.nzb";
                bool isSpaceAvailable = IsSpaceIsAvailable(e.Result.Length);

                if (isSpaceAvailable)
                {
                    // Save mp3 to Isolated Storage
                    using (var isfs = new IsolatedStorageFileStream(fileName,
                                        FileMode.CreateNew,
                                        IsolatedStorageFile.GetUserStoreForApplication()))
                    {
                        long fileLen = e.Result.Length;
                        byte[] b = new byte[fileLen];
                        var numberOfBytesRead = e.Result.Read(b, 0, b.Length);
                        isfs.Write(b, 0, numberOfBytesRead);
                        isfs.Flush();
                        isfs.Close();

                        isf = IsolatedStorageFile.GetUserStoreForApplication();
                        stream = isf.OpenFile(fileName, FileMode.Open);

                        MessageBox.Show("File downloaded successfully");

                        App.GlobalClient.UploadFileAsync("/Public/", fileName, stream, (response) =>
                            {
                                MessageBox.Show("Uploaded file to Dropbox OK.");
                            },
                         (error) =>
                         {
                             MessageBox.Show(error + "Cannot upload file to dropbox.");
                         });
                    }
                    //stream.Close();
                    isf.DeleteFile(searchBox.Text + fileExt);
                }
                else
                {
                    MessageBox.Show("Not enough to space available to download the file");
                }

            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }
        else
        {
            MessageBox.Show(e.Error.Message);
        }

    }

I cannot think where I am going wrong, but if someone could point me in the right direction, I would appreciate it.

You are trying to delete file inside using statement, where file is not closed yet

UPD: Your upload is async, so you can delete file only when it completed. Put your code near MessageBox.Show("Uploaded file to Dropbox OK.");