Mac Mini/Lion Server/Airport Extreme Won't Sleep...?

I am at a loss with this one. I have a Mid-2011 Mac Mini running OS X 10.7.4 Server (11E53) connected via gigabit ethernet to an Airport Extreme. This computer will not sleep on its own using the system sleep timer.

If anyone has any ideas that may help, I'm all ears! The Mac Mini should sleep as intended and the Airport Extreme router should wake it if network resources are requested via a Magic Packet. This same Airport Extreme does wake the other computers on the network just fine when they are configured to Wake on Lan (womp 1 in the pmset -g output, below).

The server is configured to offer the following services: file sharing, Time Machine and screen sharing.

The power saver settings on the Mac Mini are configured to sleep in 45 minutes, turn the screen off in 1 minute and wake for network access is enabled. The output of pmset -g is below for reference:

Active Profiles:

AC Power -1*

Currently in use:

hibernatemode 0

disksleep 10

womp 1

networkoversleep 0

sleep 45

powerbutton 1

ttyskeepawake 1

hibernatefile /var/vm/sleepimage

autorestart 1

panicrestart 15

displaysleep 1

If the Mac Mini is manually placed in sleep mode, via the Apple Menu or the button on the Login Screen for example, then it will sleep just fine. While the Mac Mini is sleeping, it will wake properly when the shared resources are accessed via another Mac on the network. For example, if the Macbook Pro tries to begin a Time Machine backup using the Time Machine Server on the Mac Mini, it will wake just fine and the backup will complete with no issues. The Mac Mini will not sleep again using the system sleep timer and must be manually put into sleep mode.

There is one printer (Canon MP560) installed on the Mac Mini, connected via USB, not shared on the network and no print jobs stuck in the print que.

I tried using the PleaseSleep software but that causes problems when the Mac Mini is used via Screen Sharing. When the Mac Mini is controlled remotely via Screen Sharing, PleaseSleep waits about a minute into the session and forces sleep mode, cutting the session short prematurely. This is unacceptable.

Also, there are no assertions that would prevent system idle sleep using the system sleep timer, as seen in the pmset -g assertions output below:

6/20/12 4:51:02 PM EDT

Assertion status system-wide:

PreventUserIdleDisplaySleep 0

CPUBoundAssertion 0

DisableInflow 0

ChargeInhibit 0

PreventSystemSleep 0

PreventUserIdleSystemSleep 0

ExternalMedia 0

DisableLowPowerBatteryWarnings 0

EnableIdleSleep 1

NoRealPowerSources_debug 0

UserIsActive 0

ApplePushServiceTask 0

Kernel Assertions: 0x0012

* Kernel Assertion ID = 500

Created At = 12/31/69 7:02:29 PM EST

Modified At = 12/31/69 7:00:00 PM EST

Owner ID = 0xffffff80122f0000

Level = 0

Assertions Set = None (4)

* Kernel Assertion ID = 501

Created At = 12/31/69 7:02:33 PM EST

Modified At = 6/18/12 10:34:22 PM EDT

Owner ID = 0xffffff8012302000

Level = 255

Assertions Set = None (4)

* Kernel Assertion ID = 502

Created At = 12/31/69 7:02:57 PM EST

Modified At = 6/20/12 4:05:41 PM EDT

Owner ID = 0xffffff801238ee00

Level = 0

Assertions Set = None (32)

* Kernel Assertion ID = 503

Created At = 6/18/12 10:32:27 PM EDT

Modified At = 12/31/69 7:00:00 PM EST

Owner ID = 0xffffff8011f22c00

Level = 255

Assertions Set = None (8)

* Kernel Assertion ID = 507

Created At = 6/19/12 10:56:46 PM EDT

Modified At = 12/31/69 7:00:00 PM EST

Owner ID = 0xffffff8018b1c400

Level = 255

Assertions Set = None (8)