Sitecore "random" Object reference not set to an instance of an object

Question

I was working fine with sitecore 6.5 when suddenly this morning I came to work, did a get latest version and then this error started

[NullReferenceException: Object reference not set to an instance of an object.]
   Sitecore.Shell.Applications.ContentEditor.Editors.Folder.FolderPage.Render() +358
   System.Web.UI.Control.LoadRecursive() +70
   System.Web.UI.Control.LoadRecursive() +189
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3177

also, some times I am getting this error when opening folders:

>    [InvalidOperationException: The Sitecore.Client.Device is null.]
>     Sitecore.Client.get_Device() +86    Sitecore.UIUtil.GetBrowserClassString() +326   
> Sitecore.sitecore.login.LoginPage.AddBrowserAttributes() +135   
> Sitecore.sitecore.login.LoginPage.OnPreRender(EventArgs e) +435   
> System.Web.UI.Control.PreRenderRecursiveInternal() +113   
> System.Web.UI.Page.ProcessRequestMain(Boolean
> includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
>         +4297

Any idea how to fix it ??

Answer 1

We just had this happen too. Solved by restarting the site. Not sure what caused it.