If you're using a custom master page and get an exception when trying to access the Web Analytics Reports that looks like this:
System.ArgumentException: Could not find the sitemap node with URL '/_layouts/WebAnalytics/WebAppSelection.aspx'.
The error is getting thrown from the PlaceHolderHorizontalNav, and if you clear it's contents inside you'll resolve the error:
<asp:ContentPlaceHolder id="PlaceHolderHorizontalNav" runat="server">
<!-- Remove this to fix Web Analytics Report exception
<SharePoint:AspMenu
ID="TopNavigationMenuV4"
Runat="server"
EnableViewState="false"
DataSourceID="topSiteMap"
AccessKey="<%$Resources:wss,navigation_accesskey%>"
UseSimpleRendering="true"
UseSeparateCss="false"
Orientation="Horizontal"
StaticDisplayLevels="2"
MaximumDynamicDisplayLevels="1"
SkipLinkText=""
CssClass="s4-tn"/>
<SharePoint:DelegateControl runat="server" ControlId="TopNavigationDataSource" Id="topNavigationDelegate">
<Template_Controls>
<asp:SiteMapDataSource
ShowStartingNode="False"
SiteMapProvider="SPNavigationProvider"
id="topSiteMap"
runat="server"
StartingNodeUrl="sid:1002"/>
</Template_Controls>
</SharePoint:DelegateControl>
-->
</asp:ContentPlaceHolder><sharepoint:aspmenu >