JDK7 bundles used : jdk7-b130-PIT http://rehudson.sfbay/hudsonws/deploypit/bundles/windows-i586/b255-2011-02-14_40/
OS Tested: Winxp, Win7
Browser tested: IE7/IE8/IE9
This issue was reported earlier also http://monaco.sfbay.sun.com/detail.jsf?cr=6990701 and got fixed. But it's back again using mentioned PIT bundles. Once JDK7 is removed from the windows machine then applet should be able to load using the older version of JRE present on the system. That's not true with JDK7 PIt build

Steps to reproduce
1) On windows box, install 6UR followed by JRE7
2) Load any applet using <applet> inside IE brower applet should get loaded fine using JRE7
2) Remove JRE7 and now system is left with 6UR jre only
3) Try to load same applet again and applet should get loaded fine with 6uR
If applet fails to load with 6UR then bug is reproduced