After I deleted a category, which had no products in it I received this error on the page.

A critical error has occurred.

Object reference not set to an instance of an object.

What is problem here ?

This is the error readout from event viewer.

AssemblyVersion: 5.6.0
ActiveTabID: 442
ActiveTabName: Gift Store
RawURL: /GiftStore.aspx
AbsoluteURL: /Default.aspx
AbsoluteURLReferrer: http://tymuseum.cboss-staged.com/GiftStore/tabid/442/ctl/ViewSource/ctlid/327/Default.aspx
UserAgent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727; .NET CLR 1.1.4322; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729; InfoPath.2)
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: 1c395d72-d132-4a92-80d6-70d1dac0b2e2
InnerException: Object reference not set to an instance of an object.
FileName:
FileLineNumber: 0
FileColumnNumber: 0
Method: Smith.DNN.Modules.CategoryMenu.CategoryMenu.Page_Load
StackTrace:
Message: DotNetNuke.Services.Exceptions.PageLoadException: Object reference not set to an instance of an object. ---> System.NullReferenceException: Object reference not set to an instance of an object. at Smith.DNN.Modules.CategoryMenu.CategoryMenu.Page_Load(Object sender, EventArgs e) at System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) at System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) at System.Web.UI.Control.OnLoad(EventArgs e) at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) --- End of inner exception stack trace ---

Version 3.97.0

I got the same error today but mine happened out of the blue. I made no changes to any of the pages. It was working yesterday, I went to my site today and got the error message. I deleted the categories module and error went away. I added the categories module back to the same page and no error yet. Just to give you some details about my install, I am also using version 3.97 and I have 2 stores on the same portal. One store is accessible to all users and the other is for users under a particular role. The error was on the store with limited access. I have separate categories and products for each store although categories are named the same for both stores. Each store page has the Minicart, BuyNow and Categories module. Hope this helps you figure it out. Here is the error from my event log:

AssemblyVersion: 5.6.0
PortalID: 0
PortalName: xxxxxx
UserID: 1
UserName: xxxxxx
ActiveTabID: 118
ActiveTabName: Distributor Store
RawURL: /distributors/distributorstore.aspx
AbsoluteURL: /Default.aspx
AbsoluteURLReferrer: http://www.xxxxxx.com/login.aspx?ReturnUrl=%2fdistributors%2fdistributorstore.aspx
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US) AppleWebKit/534.10 (KHTML, like Gecko) Chrome/8.0.552.224 Safari/534.10
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: 03e2f81a-ffc8-43a9-92bb-761170abb011
InnerException: Object reference not set to an instance of an object.
FileName:
FileLineNumber: 0
FileColumnNumber: 0
Method: Smith.DNN.Modules.CategoryMenu.CategoryMenu.Page_Load
StackTrace:
Message: DotNetNuke.Services.Exceptions.PageLoadException: Object reference not set to an instance of an object. ---> System.NullReferenceException: Object reference not set to an instance of an object. at Smith.DNN.Modules.CategoryMenu.CategoryMenu.Page_Load(Object sender, EventArgs e) at System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) at System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) at System.Web.UI.Control.OnLoad(EventArgs e) at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) --- End of inner exception stack trace ---