Ok, so once upon a time, my code worked. Since then I did some refactoring (basic stuff so I thought) but now I'm getting a null reference exception, and I can't bloody well figure out why.

Here's where it starts. note, this is the logout method, but all of my ActivityLogs sections are throwing this error

    Function LogOut(ByVal go As String) As ActionResult

        ActivityLogService.AddActivity(AuthenticationHelper.RetrieveAuthUser.ID, _
                                       IActivityLogService.LogType.UserLogout, _
                                       HttpContext.Request.UserHostAddress)

        ActivityLogService.SubmitChanges()

        ''# more stuff happens after this

    End Function

The service is pretty straight forward (notice the ERROR THROWN HERE)

    Public Sub AddActivity(ByVal userid As Integer, ByVal activity As Integer, ByVal ip As String) Implements IActivityLogService.AddActivity
        Dim _activity As ActivityLog = New ActivityLog With {.Activity = activity,
                                                             .UserID = userid,
                                                             .UserIP = ip.IPAddressToNumber,
                                                             .ActivityDate = DateTime.UtcNow}

        ActivityLogRepository.Create(_activity)  ''#ERROR THROWN HERE
    End Sub

And the Interface that the Service uses looks like this

Public Interface IActivityLogService
    Sub AddActivity(ByVal userid As Integer, ByVal activity As Integer, ByVal ip As String)
    Function GetUsersLastActivity(ByVal UserID As Integer) As ActivityLog
    Sub SubmitChanges()

    ''' <summary>
    ''' The type of activity done by the user
    ''' </summary>
    ''' <remarks>Each int refers to an activity.  
    ''' There can be no duplicates or modifications 
    ''' after this application goes live</remarks>
    Enum LogType As Integer
        ''' <summary>
        ''' A new session started
        ''' </summary>
        SessionStarted = 1
        ''' <summary>
        ''' A new user is Added/Created
        ''' </summary>
        UserAdded = 2
        ''' <summary>
        ''' User has updated their profile
        ''' </summary>
        UserUpdated = 3
        ''' <summary>
        ''' User has logged into they system
        ''' </summary>
        UserLogin = 4
        ''' <summary>
        ''' User has logged out of the system
        ''' </summary>
        UserLogout = 5
        ''' <summary>
        ''' A new event has been added
        ''' </summary>
        EventAdded = 6
        ''' <summary>
        ''' An event has been updated
        ''' </summary>
        EventUpdated = 7
        ''' <summary>
        ''' An event has been deleted
        ''' </summary>
        EventDeleted = 8
        ''' <summary>
        ''' An event has received a Up/Down vote
        ''' </summary>
        EventVoted = 9
        ''' <summary>
        ''' An event has been closed
        ''' </summary>
        EventCloseVoted = 10
        ''' <summary>
        ''' A comment has been added to an event
        ''' </summary>
        CommentAdded = 11
        ''' <summary>
        ''' A comment has been updated
        ''' </summary>
        CommentUpdated = 12
        ''' <summary>
        ''' A comment has been deleted
        ''' </summary>
        CommentDeleted = 13
        ''' <summary>
        ''' An event or comment has been reported as spam
        ''' </summary>
        SpamReported = 14
    End Enum
End Interface

And the repository is equally straight forward

    Public Sub Create(ByVal activity As ActivityLog) Implements IActivityLogRepository.Create
        dc.ActivityLogs.InsertOnSubmit(activity)
    End Sub

The stack trace is as follows

[NullReferenceException: Object reference not set to an instance of an object.] MyApp.Core.Domain.ActivityLogService.AddActivity(Int32 userid, Int32 activity, String ip) in E:\Projects\MyApp\MyApp.Core\Domain\Services\ActivityLogService.vb:49 MyApp.Core.Controllers.UsersController.Authenticate(String go) in E:\Projects\MyApp\MyApp.Core\Controllers\UsersController.vb:258 lambda_method(Closure , ControllerBase , Object[] ) +163 System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters) +51 System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary2 parameters) +409 System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary2 parameters) +52 System.Web.Mvc.<>c_DisplayClass15.b_12() +127 System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func1 continuation) +436 System.Web.Mvc.<>c__DisplayClass17.<InvokeActionMethodWithFilters>b__14() +61 System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodWithFilters(ControllerContext controllerContext, IList1 filters, ActionDescriptor actionDescriptor, IDictionary2 parameters) +305 System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName) +830 System.Web.Mvc.Controller.ExecuteCore() +136 System.Web.Mvc.ControllerBase.Execute(RequestContext requestContext) +232 System.Web.Mvc.ControllerBase.System.Web.Mvc.IController.Execute(RequestContext requestContext) +39 System.Web.Mvc.<>c__DisplayClassb.<BeginProcessRequest>b__5() +68 System.Web.Mvc.Async.<>c__DisplayClass1.<MakeVoidDelegate>b__0() +44 System.Web.Mvc.Async.<>c__DisplayClass81.b__7(IAsyncResult ) +42 System.Web.Mvc.Async.WrappedAsyncResult`1.End() +141 System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, Object tag) +54 System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, Object tag) +40 System.Web.Mvc.<>c_DisplayClasse.b_d() +61 System.Web.Mvc.SecurityUtil.b_0(Action f) +31 System.Web.Mvc.SecurityUtil.ProcessInApplicationTrust(Action action) +56 System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +110 System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) +38 System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +690 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +194

here's an image of the error when attached to the debugger.

And here's an image of the DB schema in question

Can anyone shed some light on what I might be missing here?