Mac refuses to sleep: Reset PreventSystemSleep?

For the last month, my Mac has refused to go to sleep – even when commanding it to do so. The screen goes black, but the computer is still on.

I have checked Apple's support page and made sure that the Energy Saver settings are correct. I've also checked under the Energy tab in Activity Monitor and can't find anything that is Preventing Sleep. I have followed the instructions to reset the SMC and NVRAM.

In Terminal, when I do pmset -g assertions I get these results:

Assertion status system-wide:
   BackgroundTask                 1
   ApplePushServiceTask           0
   UserIsActive                   1
   PreventUserIdleDisplaySleep    0
   PreventSystemSleep             1
   ExternalMedia                  0
   PreventUserIdleSystemSleep     0
   NetworkClientActive            0

Listed by owning process:
   pid 111(hidd): [0x0000014d00090344] 00:08:52 UserIsActive named: "com.apple.iohideventsystem.queue.tickle" 
    Timeout will fire in 367 secs Action=TimeoutActionRelease
   pid 55(configd): [0x0000005f0007016b] 00:12:50 DenySystemSleep named: "InternetSharingPreferencePlugin" 
   pid 42(UserEventAgent): [0x0000006d000b0170] 00:12:36 BackgroundTask named: "com.apple.metadata.mds_stores.power" 
    Created for PID: 232. 
Kernel Assertions: 0x10c=USB,BT-HID,MAGICWAKE
   id=501  level=255 0x4=USB mod=01/01/70 01:00 description=com.apple.usb.externaldevice.fd140000 owner=USB Receiver
   id=502  level=255 0x4=USB mod=01/01/70 01:00 description=com.apple.usb.externaldevice.fa120000 owner=IOUSBHostDevice
   id=503  level=255 0x4=USB mod=01/01/70 01:00 description=com.apple.usb.externaldevice.fa130000 
   id=505  level=255 0x100=MAGICWAKE mod=01/01/70 01:00 description=en0 owner=en0
   id=506  level=255 0x100=MAGICWAKE mod=01/01/70 01:00 description=en1 owner=en1
   id=507  level=255 0x8=BT-HID mod=01/01/70 01:00 description=com.apple.driver.IOBluetoothHIDDriver owner=BNBTrackpadDevice
   id=508  level=255 0x8=BT-HID mod=01/01/70 01:00 description=com.apple.driver.IOBluetoothHIDDriver owner=AppleBluetoothHIDKeyboard
Idle sleep preventers: IODisplayWrangler

PreventSystemSleep is active 1 for some reason.

Misc. info:

• I had the old Caffeine app installed and made sure it wasn't active and then uninstalled the application. I'm not sure how to check if the system is "caffeinated", but I don't think caffeinate is stuck.
• I've tried shutting down my other network devices while troubleshooting and don't believe that there is some network service causing the problem.

Is there a way to check what's keeping PreventSystemSleep active? Is there a way to disable it?

Solution 1:

From your sleep assertions, it appears you have Internet Sharing enabled. Try disabling it via  → System Preferences → Sharing → Internet Sharing.

Solution 2:

In some cases, an unprinted document in offline printer could cause issues like this.

To try to solve this problem, go to System Preferences → Printers & Scanners and delete offline printers.