Hello,
I as far as I remember in CRM 4.0/2011 time mentioned code was used to show/hide navigation items located at the left side of CRM Entity form. Since 2013 (and it is supported now for 2015/2016) we have got supported approach to show/hide navigation items.
Try to replace mentioned code with following:
Xrm.Page.ui.navigation.items.get("ava_ava_country_ava_riskmanagement").setVisible(false);
Dynamics CRM MVP
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