One of my test users (jsmith) suddenly cannot make any posts and gets an error message, here is the data from the event viewer:

ModuleId: 1738
ModuleDefId: 107
FriendlyName: Add/Edit Post
ModuleControlSource: DesktopModules/Forum/Forum_PostEdit.ascx
AssemblyVersion: 04.07.00
PortalID: 4
PortalName: Northstar Camaro Club Forum
UserID: 20
UserName: jsmith
ActiveTabID: 487
ActiveTabName: NCC Forum
RawURL: /forum/NCCForum/tabid/487/ctl/PostEdit/forumid/28/action/new/mid/1738/Default.aspx
AbsoluteURL: /Default.aspx
AbsoluteURLReferrer: http://www.northstarcamaroclub.net/forum/NCCForum/tabid/487/forumid/28/scope/threads/Default.aspx
UserAgent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.04506.648)
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: 55dc903c-f69f-424b-9ced-68c6b9d7bbe2
InnerException: Object reference not set to an instance of an object.
FileName:
FileLineNumber: 0
FileColumnNumber: 0
Method: DotNetNuke.Modules.Forum.PostEdit.Page_Load
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.PostEdit.Page_Load(Object sender, EventArgs e) --- End of inner exception stack trace ---
Source:
Server Name: WEBD19

How do I fix it so this user can add/edit threads again?

Actually, the user just started working again about an hour ago.  I haven't posted that, because I don't know why he broke, or why he started working again.  Crazy....