500 error on calling sitemap

[theRealKarlos]

Hi - I believe my Orchard version is 1.6. I've tried both versions 1.5 and 1.6 of advanced sitemap and both produce a 500 error for /sitemap and /sitemap.xml.

My Orchard install is customised and maybe this is the problem, I just wondered if anyone had any bright ideas for me to try or a place I should be looking to resolve this issue.

I don't seem to have the Output Cache module installed.

I have found this log entry which I guess is related to my issue:
2013-10-17 13:21:21,029 [28] Orchard.Exceptions.DefaultExceptionPolicy - An unexpected exception was caught
System.NullReferenceException: Object reference not set to an instance of an object.
at WebAdvanced.Sitemap.Services.AdvancedSitemapService.b__1f(AcquireContext1 ctx) in d:\Websites\***********.co.uk\htdocs\Modules\WebAdvanced.Sitemap\Services\AdvancedSitemapService.cs:line 210 at Orchard.Caching.Cache2.CreateEntry(TKey k, Func2 acquire) in E:\Docs\Visual Studio 2010\Orchard\src\Orchard\Caching\Cache.cs:line 57 at Orchard.Caching.Cache2.<>c__DisplayClass2.b__0(TKey k) in E:\Docs\Visual Studio 2010\Orchard\src\Orchard\Caching\Cache.cs:line 19
at System.Collections.Concurrent.ConcurrentDictionary2.AddOrUpdate(TKey key, Func2 addValueFactory, Func3 updateValueFactory) at Orchard.Caching.Cache2.Get(TKey key, Func2 acquire) in E:\Docs\Visual Studio 2010\Orchard\src\Orchard\Caching\Cache.cs:line 17 at Orchard.Caching.DefaultCacheManager.Get[TKey,TResult](TKey key, Func2 acquire) in E:\Docs\Visual Studio 2010\Orchard\src\Orchard\Caching\DefaultCacheManager.cs:line 33
at WebAdvanced.Sitemap.Services.AdvancedSitemapService.GetRoutes() in d:\Websites**************.co.uk\htdocs\Modules\WebAdvanced.Sitemap\Services\AdvancedSitemapService.cs:line 197
at WebAdvanced.Sitemap.Services.AdvancedSitemapService.GetSitemapRoot() in d:\Websites****************.co.uk\htdocs\Modules\WebAdvanced.Sitemap\Services\AdvancedSitemapService.cs:line 271
at WebAdvanced.Sitemap.Controllers.HomeController.Index() in d:\Websites***************.co.uk\htdocs\Modules\WebAdvanced.Sitemap\Controllers\HomeController.cs:line 109
at lambda_method(Closure , ControllerBase , Object[] )
at System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters)
at System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary2 parameters) at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary2 parameters)
at System.Web.Mvc.ControllerActionInvoker.<>c__DisplayClass13.b__10()
at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func1 continuation) at System.Web.Mvc.ControllerActionInvoker.<>c__DisplayClass13.<>c__DisplayClass15.<InvokeActionMethodWithFilters>b__12() at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func1 continuation)
at System.Web.Mvc.ControllerActionInvoker.<>c__DisplayClass13.<>c__DisplayClass15.b__12()
at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation)

Any help appreciated.

Thanks