More than once I've received errors similar to the following when installing packages on (Umbraco 7.4.0):

Server Error in '/' Application.

The task runner has completed.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.InvalidOperationException: The task runner has completed.

Source Error:

Line 200:
Line 201:                // add task
Line 202:                _logger.Debug<BackgroundTaskRunner>(_logPrefix + "Task added {0}", task.GetType);
Line 203:                _tasks.Add(task);
Line 204:

Source File: D:\src\Applications\Umbraco-CMS-git\src\Umbraco.Web\Scheduling\BackgroundTaskRunner.cs    Line: 202 

Stack Trace:

[InvalidOperationException: The task runner has completed.]
   Umbraco.Web.Scheduling.BackgroundTaskRunner`1.Add(T task) in D:\src\Applications\Umbraco-CMS-git\src\Umbraco.Web\Scheduling\BackgroundTaskRunner.cs:202
   Umbraco.Web.Strategies.ServerRegistrationEventHandler.RegisterServer(UmbracoRequestEventArgs e) in D:\src\Applications\Umbraco-CMS-git\src\Umbraco.Web\Strategies\ServerRegistrationEventHandler.cs:94
   Umbraco.Web.Strategies.ServerRegistrationEventHandler.UmbracoModuleRouteAttempt(Object sender, RoutableAttemptEventArgs e) in D:\src\Applications\Umbraco-CMS-git\src\Umbraco.Web\Strategies\ServerRegistrationEventHandler.cs:74
   System.EventHandler`1.Invoke(Object sender, TEventArgs e) +0
   Umbraco.Web.UmbracoModule.OnRouteAttempt(RoutableAttemptEventArgs args) in D:\src\Applications\Umbraco-CMS-git\src\Umbraco.Web\UmbracoModule.cs:537
   Umbraco.Web.UmbracoModule.ProcessRequest(HttpContextBase httpContext) in D:\src\Applications\Umbraco-CMS-git\src\Umbraco.Web\UmbracoModule.cs:117
   Umbraco.Web.UmbracoModule.<Init>b__12_3(Object sender, EventArgs e) in D:\src\Applications\Umbraco-CMS-git\src\Umbraco.Web\UmbracoModule.cs:506
   System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +142
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +92

Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.6.1055.0

In this particular instance I was installing "301 URL Tracker", but it's happened with a couple other packages in the past as well. What could be causing this?