NullReference Exception after upgrade to7.0.5

[triplw]

Upgraded from 7.0.3 to 7.0.5 without any errors during installation. The next day I started getting NullReferenceException (see stack below) errors a couple times/day.
Right before the server error the buttons at the top of the Admin pages disappear. Restarting the app will get the site running again.
Can anyone help?

Stack Trace:

[NullReferenceException: Object reference not set to an instance of an object.]
Layouts_AdminPanel.Page_Init(Object sender, EventArgs e) +20
System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) +14
System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) +35
System.Web.UI.Control.OnInit(EventArgs e) +99
System.Web.UI.UserControl.OnInit(EventArgs e) +77
System.Web.UI.Control.InitRecursive(Control namingContainer) +333
System.Web.UI.Control.InitRecursive(Control namingContainer) +210
System.Web.UI.Control.InitRecursive(Control namingContainer) +210
System.Web.UI.Control.InitRecursive(Control namingContainer) +210
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +378

[triplw]

Haven't had any more problems. It must have been a problem with my shared server.