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

Question

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)

Answer 1

I Have the same issue with pleasesleep.
No ARD Session without sleep ;-)
My stup is a little bit different to yours.
My MacMini act as an HTPC for Plex and it dosent sleep as well.
I guess it has something to to with External USB HDDs or in your case printers or USB Hubs or etc. etc.
I found a AppleScript called Nacrolepsy 2.0
It dosent work probebly right now but I hope It could be a solution in the near future.
Take a look at
http://blog.schreiter.info/narcolepsy-2-0-for-mac-os-x/