I have this error in my log table when publishing a node.

Error adding node with url 'Your Week-by-Week Guide' to SiteMapProvider: System.Collections.Generic.KeyNotFoundException: The given key was not present in the dictionary.     at System.Collections.Generic.Dictionary`2.get_Item(TKey key)     at umbraco.presentation.nodeFactory.UmbracoSiteMapProvider.UpdateNode(Node node)

Any idea what this is?  What is the Umbracositemap provider? What purpose does it serve?  Running umbraco 4.5.2