C# Winforms Backgroundworker error - object not set to an instance of object

Question

I have a winforms file search application that runs with no errors in visual studio, but when i publish it i get a "object not set to an instance of object error"

The backgroundworker code which is the point where it fails is :

    private void backGroundWorker_DoWork(object sender, DoWorkEventArgs e)
    {
        e.Result = RunSearch();
        PopulateUi((FilteredList)e.Result);
    }

    private void backGroundWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        try
        {
                var ans = (FilteredList)e.Result;
                toolStripStatusLabel1.Text += "Folders found: " + ans.FolderCount + " | Files found: " + ans.FileCount;

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

The messagebox shows the exception text.What do i need to do to correct this?

EDIT This question is different to the one referred to above as its about a concurrency issue and not simply an object being null. As stated above, the application runs with no errors before publishing.

thanks

Edit 2

I have tried creating a private object ( _x) in the class and assigning the result to it, but it still shows as null in the RunWorkerCompleted function. The edited code looks like this:

    private void backGroundWorker_DoWork(object sender, DoWorkEventArgs e)
    {
        e.Result = RunSearch();
        _x = e.Result;
        PopulateUi((FilteredList)e.Result);
    }

    private void backGroundWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        try
        {
            if (_x == null)
            {
                MessageBox.Show("e is null");
            }

            var ans = (FilteredList)_x;
            toolStripStatusLabel1.Text += "Folders found: " + ans.FolderCount + " | Files found: " + ans.FileCount;
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }
    }