In the system log there are multiple instances of this all the time: ACPI Error: No installed handler for fixed event  (20090903/evevent-306). I think it may be related to the WiFi chipset, an r8192se_pci module, because there is an occasional "rtl8192_hw_sleep_down(): RF Change in progress!
rtl8192_hw_wakeup(): RF Change in progress! schedule wake up task again" logged, but I don't know how to diagnose it. It doesn't appear to be causing any problems.