I could reproduce this issue on multiple machines. Moslty happenes on Vista and Win 7.

How to reprodcue this issue:
1. Install 6u18
2. Make sure installation goes fine.
3. Set the registry for auto update
[HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Update\Policy]
"UpdateServletURL"="http://j2se.east.sun.com/arc/1.6.0_18/nightly/2009-09-29/windows-i586/map.xml"

4.) Launch jusched.exe and wait for 5-6 mins

Expected behavior:
Update Balloon should be shown in the system tray

Actual Behavior:
No Update balloon is shown.
 ------------------ jusched.log file on Vista ---------------------


Mon Oct 05 15:10:06 2009
:: RegQueryValueEx(Country): Error:6, ErrorCode:0

Mon Oct 05 15:10:06 2009
:: Save Country Code US after GetCountry()
Mon Oct 05 15:11:44 2009
:: InstallStatus:ret=200 visid=3430d7454-ac9fe9e604 prop21=3430d7454-ac9fe9e604 method=joff state=ic ver=XX,1.6.0_18-b503 installerver=t ICstatus=;jre|0
<?xml version="1.0" encoding="UTF-8"?>
<status>SUCCESS</status>

Mon Oct 05 15:11:51 2009
:: InstallStatus:ret=200 visid=3430d7454-ac9fe9e604 prop21=3430d7454-ac9fe9e604 method=joff state=ic ver=XX,1.6.0_18-b503 installerver= ICstatus=;jre|0
<?xml version="1.0" encoding="UTF-8"?>
<status>SUCCESS</status>

Mon Oct 05 15:17:33 2009
:: **************** Running jusched ****************

Mon Oct 05 15:17:33 2009
:: GetJavaFXUpdateTimeKey: returning FALSE

Mon Oct 05 15:17:33 2009
:: GetJavaFXUpdateTimeKey: returning FALSE

Mon Oct 05 15:17:33 2009
:: GetJavaFXUpdateTimeKey: returning FALSE

Mon Oct 05 15:17:33 2009
:: No valid LastFinishTime && <4 days past LastSched, sleeping until next 1hr window (7-hr delay): Mon Oct 05 18:02:00 2009

Mon Oct 05 15:17:33 2009
:: JavaUpdate NextSchedTime=Mon Oct 19 06:15:00 2009
JavaFXUpdate NextSchedTime=Sat Oct 10 10:02:00 2009
JavaFX: lastSchedTime=Sat Oct 03 10:02:00 2009
JavaFX: nextSchedTime=Sat Oct 10 10:02:00 2009
JavaFX: sleeptime (sec=9896, hours=2)
actual sleep time=9896689 msecs (2:44:56) for JavaFX