IMac7.1 (10.7.5) Random Sleep Cause:-100

Question

I have an iMac 7.1 (2007) The OS is (10.7.5). It has taken to going to sleep periodically. When I click the mouse, it will wake back up. Of course whatever was processing is halted and the wireless connection is dropped.
Whenever this happens, if I check the console logs, I get a log statement such as:
                   kernel: Previous Sleep Cause: -100
This is not the power management settings, the computer is set to never sleep and to not dim the display for hours. The sleep will happen when using the system. I had thought it was related to graphics as it had happened more with the videos. It has since proven to happen even if just listening to music on iTunes. (I think I have noticed it happens more frequently when synching an iPhone/iPod but not all of the time.)
I haven taken into the geniuses twice and left it overnight. The issue could not be replicated at the store. The system diagnostic scan shows the components as healthy. I was encouraged to look for something environmental. There was some thought that it may be a power supply but this was just a guess and the power supply does not fail diagnostics.
Virus scanning turns up nothing.
I have taken all accessorries off the system other than the USB keyboard and mouse and a single USB cable for iPhone/iPod. This includes disabling and unplugging the time machine.
I have put a UPS between the system and the wall with no other components on the UPS to rule out poor power input or low quality power. This shows the output remains between 121 and 125 V and 0.105 Kw at 60 Hz.
Using istat pro from bjango, i see no particular pattern on the system operating conditions when the failure occurs.
After the above, the problem has become less frequent but still occurs.
output from pmset -g is:
Active Profiles:
AC Power                    -1*
Currently in use:
autorestart          1
powerbutton          1
halfdim          1
panicrestart          157680000
hibernatefile          /var/vm/sleepimage
networkoversleep          0
disksleep          0
sleep                    0
hibernatemode          0
ttyskeepawake          1
displaysleep          180
womp                    0
The memory, disks, etc, have not changed. The only changes have been periodic S/W updates and time. Powersupply was replaced by Apple 25 months ago.
Any suggestions?

Answer 1

After reading other threads, I decided to run memtest to verify the memory in single user mode. The system passed.
I also upgraded to Mountain Lion 10.8.2 and applied any subsequent updates. I also re-enabled the timemachine.
I noticed this changes the type of messages in the logs. I have had one failure after the update:
12/29/12 3:46:15.363 AM com.apple.usbmuxd[41]: stopping.
12/29/12 3:46:15.518 AM com.apple.usbmuxd[1893]: usbmuxd-296.3 on Jul 25 2012 at 00:28:37, running 64 bit
12/29/12 3:50:42.000 AM kernel[0]: CODE SIGNING: cs_invalid_page(0x1000): p=1945[GoogleSoftwareUp] clearing CS_VALID
12/29/12 4:12:50.818 AM com.apple.backupd[1328]: Copied 3.7 GB of 12.1 GB, 241337 of 311675 items
12/29/12 4:13:33.474 AM WindowServer[104]: Created shield window 0x1ad for display 0x04271b00
12/29/12 4:13:33.474 AM WindowServer[104]: device_generate_desktop_screenshot: authw 0x0(0), shield 0x0(0)
12/29/12 4:13:33.489 AM WindowServer[104]: device_generate_lock_screen_screenshot: authw 0x0(0), shield 0x0(0)
12/29/12 4:13:33.685 AM com.apple.time[11]: Next maintenance wake [Backup Interval]: <date: 0x7fe5eb61d300> Sat Dec 29 05:12:24 2012 PST (approx)
12/29/12 4:13:33.685 AM com.apple.time[11]: Requesting maintenance wake [Backup Interval]: <date: 0x7fe5eb61d300> Sat Dec 29 05:12:24 2012 PST (approx)
12/29/12 4:13:35.000 AM kernel[0]: PM mode before entering WoW is 1 and PM allowed state is 1
12/29/12 4:44:51.000 AM kernel[0]: Wake reason: EHC1
12/29/12 4:44:51.000 AM kernel[0]: Previous Sleep Cause: -100
12/29/12 4:44:51.000 AM kernel[0]: The USB device Keyboard Hub (Port 1 of Hub at 0xfd000000) may have caused a wake by issuing a remote wakeup (2)