I noticed a lot of the following events in a Windows event log:

Event ID: 16398 Bits-Client
A new BITS job could not be created.

Using Powershell is the best way to deal with this:

PS> Import-Module BitsTransfer

To list the entries (This should be 60 is you are getting the 16398 event, and the default has not been changed.):

PS> Get-BitsTransfer

To remove all the entries:

PS> Get-BitsTransfer -AllUsers | Remove-BitsTransfer

Using the legacy bitsadmin command:
This will display all the queue entries:

C:\> bitsadmin /List /AllUsers

You should see 60, if you are getting this message in the logs, since that is the default.

C:\> bitsadmin /AllUsers /Reset

Do a list again to verify that all have been canceled.

If that does not work, you do the following:

C:\> net stop Bits
C:\> cd C:\Users\All Users\AppData\Microsoft\Network\Downloader

Delete all the qmgr*.dat files in the directory:

C:\> del qmgr*.dat

Start the Background Intelligent Transfer Queue service:

C:\> net start Bits