backgroundcontainer.dll is a notorious malware, so it was probably removed by an antivirus. To remove the error, try this:
- Press (Win)+R
- Type
taskschd.msc
- Press the Enter key
- Click on the Task Scheduler Library folder
- Right-click on the BackgroundContainer task
- Select "Delete”
(Instructions originally by GreginMich on Microsoft Answers: http://answers.microsoft.com/en-us/protect/forum/protect_other-protect_scanning/error-message-on-start-up-windows-8/7f29c7ad-2d55-4f1c-8110-ddca3902f596)
After this is done, update your antivirus' definitions and run a full PC scan to be safe.