How can I fix a NullReferenceException in System.Windows.Forms.ToolStripControlHost.SetVisibleCore ?

Question

When setting control visibility I sometimes get this:

CRASH! Failed to refresh job control:
Exception:NullReferenceException
Message:Object reference not set to an instance of an object.
Source:     System.Windows.Forms
TargetSite: SetVisibleCore
StackTrace:    at System.Windows.Forms.ToolStripControlHost.SetVisibleCore(Boolean visible)
   at System.Windows.Forms.ToolStripItem.set_Visible(Boolean value)
   at Cwc.WaterWorks.Console.frmMain.SetToolStripOptionalButtons()
   at Cwc.WaterWorks.Console.frmMain.UpdateToolStrip(ToolStripButton toolStripButton)
   at Cwc.WaterWorks.Console.frmMain.RefreshJobControl(Boolean fetch)

Called from:

private void SetToolStripOptionalButtons()
{

    NewJobButtonsVisibility(newJobStripButton.Checked);
    JobListButtonsVisibility(jobListStripButton.Checked);
    jumpToJob.Visible = !newJobStripButton.Checked;

    if (newJobStripButton.Checked)
    {
        JobCreateStatus(false);
            uxLockedToolStrip.Visible = false;
        HideJobControlButtons();
    }
    else if (jobListStripButton.Checked)
    {
        UpdateFilterStatus();
        HideJobControlButtons();
    }
        else if (controlStripButton.Checked)
    {
        ShowJobControlButtons();
        }

        findCustomerStripButton.Enabled = newJobStripButton.Checked && basis2ServiceLayer.Basis2Status.IsConnected==true;
    filterStripDropDown.Enabled = jobListStripButton.Checked;
}

Any ideas why?