I know that this error has occurred before, but it seems that there are various reasons. So, maybe someone can shed some light on my problem, since previously reported errors dont appear to be the same.

I have DNN 4.9
AssemblyVersion: 04.09.02

Here is an error log from the events viewer. I get a LOT of these...Can someone help debug this one please.

ActiveTabName: Hjem
RawURL: /Default.aspx
AbsoluteURL: /Default.aspx
AbsoluteURLReferrer:
UserAgent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; .NET CLR 2.0.50727; .NET CLR 1.1.4322; InfoPath.2; .NET CLR 3.0.04506.648; .NET CLR 3.5.21022; .NET CLR 3.0.4506.2152; OfficeLiveConnector.1.3; OfficeLivePatch.0.0; .NET CLR 3.5.30729)
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: 33a0f38b-5f2f-4e95-8530-5d5dc8af61e5
InnerException: Object reference not set to an instance of an object.
FileName:
FileLineNumber: 0
FileColumnNumber: 0
Method: DotNetNuke.Modules.Events.SelectCategory.get_SelectedCategory
StackTrace:
Message: DotNetNuke.Services.Exceptions.ModuleLoadException: Object reference not set to an instance of an object. ---> System.NullReferenceException: Object reference not set to an instance of an object. at DotNetNuke.Modules.Events.SelectCategory.get_SelectedCategory() at DotNetNuke.Modules.Events.EventList.BindDataGrid() at DotNetNuke.Modules.Events.EventList.Page_Load(Object sender, EventArgs e) --- End of inner exception stack trace ---
 

Yes, it is the events module.

It is version 03.03.08

This (3.3.8) is an old verison that has been updated. Numerous bugs have been fixed. Have a look at the latest version 5.0.3 (http://dnnevents.codeplex.com) and install this one to replace your current version.