Exception has been thrown by the target of an invocation.

I am in Geocortex Essential 3.12.0. 

I was trying to open a particular site to edit in Geocortex Essential Manager, but ran into this "Exception has been thrown by the target of an invocation" error, and was not able to open the site at all.  The error message screen is attached here. 

/customer/servlet/servlet.FileDownload?file=00P6000000e88SSEAY

 

And the full StackTrace is here: 

   at Geocortex.Essentials.Configuration.Models.SiteConfig.ConfigureSite(Site site)

 

   at Geocortex.Essentials.Configuration.Models.SiteConfig.ToBusinessObject()

 

   at Geocortex.Essentials.RestManager.Models.Repositories.SessionSiteRepository.GetConversionResult(SiteConfig siteConfig)

 

   at Geocortex.Essentials.RestManager.ActionFilters.SiteCheckFilterAttribute.OnActionExecuting(ActionExecutingContext filterContext)

 

   at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation)

 

   at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation)

 

   at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation)

 

   at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation)

 

   at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodWithFilters(ControllerContext controllerContext, IList`1 filters, ActionDescriptor actionDescriptor, IDictionary`2 parameters)

 

   at System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName)

 

Anybody can help me dignose to see what is wrong this this site? 

 

Thanks,

Jie