Why can't I see the 'Visitors and Sessions' report?
Getting the Visitors and Sessions report to display in Urchin 4 requires the use of the Urchin Traffic Monitor (UTM) which is included in the base product. The UTM requires special configuration and settings that are detailed in the White Paper on "Urchin Tracking Module (UTM)". Please see the white papers section of the Urchin help center for more details.
The reason this report is not visible without the UTM enabled is because there is no way for Urchin to identify Unique visitors without it. And the Visitors and Sessions reports relate specifically to Unique visitors.
You can still view statistics on the visitor Sessions "only" by selecting the "Traffic"; "Daily Graph" report. The default tab displays the total Visitor Sessions for every day and can be viewed in an hourly, daily or monthly format.