"The same key was already used for another template!'

I keep getting the following error:

```

System.InvalidOperationException

The same key was already used for another template!

System.InvalidOperationException: The same key was already used for another template!
at RazorEngine.Templating.DelegateTemplateManager.<>c__DisplayClass1.b__0(ITemplateKey k, ITemplateSource oldSource)
at System.Collections.Concurrent.ConcurrentDictionary`2.AddOrUpdate(TKey key, TValue addValue, Func`3 updateValueFactory)
at RazorEngine.Templating.DelegateTemplateManager.AddDynamic(ITemplateKey key, ITemplateSource source)
at RazorEngine.Templating.TemplateService.GetKeyAndAdd(String template, String name)
at RazorEngine.Templating.TemplateService.GetTemplate(String razorTemplate, Object model, String cacheName)
at RazorEngine.Templating.TemplateService.Parse(String razorTemplate, Object model, DynamicViewBag viewBag, String cacheName)
at RazorEngine.Razor.Parse(String razorTemplate, Object model, String cacheName)
at Postal.FileSystemRazorView.Render(ViewContext viewContext, TextWriter writer)
at Postal.EmailViewRenderer.RenderView(IView view, ViewDataDictionary viewData, ControllerContext controllerContext, ImageEmbedder imageEmbedder)
at Postal.EmailViewRenderer.Render(Email email, String viewName)
at Postal.EmailService.CreateMailMessage(Email email)
at Postal.EmailService.Send(Email email)
```

I am not sure why?

I am using hangfire to send email as background job.