I have installed ASP.NET hotfix and I find that Startup Type of the ASP.NET Session State Service is set to Manual.Why?

Microsoft has acknowledged this as a Bug
To set the StartUp Type as desired refer following steps

1. In Control Panel, open Administrative Tools.
2. Click Services. The Services window appears.
3. Expand the Name column so that the complete name of each service appears.

   Note A Startup Type column displays the current Startup Type value for each service.

4. Double-click the ASP.NET State Service service. The ASP.NET State Service Properties window appears.
5. On the General tab, click one of the following options in the Startup type list:
   • Manual
   • Automatic
   • Disabled
6. Click Apply, and then click OK to save your settings.

   In the Services window, notice your changes to the Startup Type in the Startup Type column.