I get this problem when i log in as host or either admin and select "my setting". How could this happen? Any comment or suggestion? Thanks.

I am using DNN 4.04 with XP pro SP2 and sql 2000.

As I log in as admin or host i can view and edit normal user via forum admin>forum user well. After i grant the user the role of  moderator or admin, the error appear. The error log shown below:

ModuleId: 399
ModuleDefId: 102
FriendlyName: User Settings
ModuleControlSource: DesktopModules/Forum/Forum_UserSettings.ascx
AssemblyVersion: 04.04.00
PortalID: 0
PortalName: My Website
UserID: 3
UserName: aaaaaaa
ActiveTabID: 62
ActiveTabName: Forum
RawURL: /a/Forum/tabid/62/ctl/UserSettings/mid/399/userid/3/Default.aspx
AbsoluteURL: /a/Default.aspx
AbsoluteURLReferrer: http://localhost/a/Forum/tabid/62/ctl/usermanage/mid/399/Default.aspx
UserAgent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; SIMBAR={01E7DF9E-7DDE-4cf5-857E-2C7321DD6B40}; .NET CLR 2.0.50727)
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: 2cae6aae-8d99-430a-a08c-05a3f81bb560
InnerException: Object reference not set to an instance of an object.
FileName:
FileLineNumber: 0
FileColumnNumber: 0
Method: DotNetNuke.Modules.Forum.UserSettings.SelectMultiTreeItems
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.Forum.UserSettings.SelectMultiTreeItems(DnnTree objTree, Int32 ForumID) at DotNetNuke.Modules.Forum.UserSettings.Page_Load(Object sender, EventArgs e) --- End of inner exception stack trace ---

Is that the both issues related? Thks for any advise.