The only way that I am able to replicate this issue is when the NavigationControl uses StartingNodeUrl which does not exist in the current culture and this is what the error says - there is not node in the SiteMap.
1. Have you added your navigation control on a page or it is inside the template?
2. Which is the language version under which you created a template and added the control?
3. Which is the language version under which you browse the page when the error appear?
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