"There is a management task (id:9920) scheduled to be run" message during shutdown or restart

Hello,

I'm sorry to posting this question in the wrong section.

I write to you about a issue when I shutdown or restart my Mac Pro.

My Mac Pro is:

-Mac Pro (late 2013) with OS X El Capitan (10.11.6)

-Processor 3.5 GHz-6-Core Intel Xeon E5

-Memory 32 GB 1866 MHz DDR3 ECC

-Startup Disk Macintosh HD

-Graphics AMD FirePro D500 3072 MB

I have upgraded recently this from OS X Mavericks to El Capitan and when I try to shutdown or restart my Mac, during shutdown appear a popup window with this message "There is a management task (id:9920) scheduled to be run". I do click on "Dismiss" button, as shown in the image attached, and the shutdown process remain completly freeze. I can move only the mouse and to force Mac to shutdown is press the turn on button for some seconds located on Mac Pro.

I remember that this problem doesn't appear in OS X Mavericks and it happen in my new Macs Pro (with the same features), never upgraded.

Please, someone can you help me??

Thanks you very much,

Giordano08