Note: This 6u12 b02 was built as a Patch-In-Place from 6u1 b02.

Windows XP Pro, 32-bit system.
6u7 is installed.
Install 6u11 b03 (http://jre.sfbay/java/re/jdk/6u11/promoted/fcs/b03/bundles/windows-i586/jre-6u11-fcs-bin-b03-windows-i586-p-10_nov_2008.exe)
Install 6u12 b02 (http://j2se.east/arc/1.6.0_12/nightly/2008-11-20/windows-i586/jre-6u12-windows-i586-p-iftw.exe)

Expected: 6u11 b03 would be uninstalled and 6u12 b02 would be installed.

Actual: 6u12 b02 errors with Error 1606.Could not access network location 0.

Attaching MSI log MSIf1b.LOG. I saw this on my machine and was able to duplicate it.
Installing 6u11 b03 (http://jre.sfbay/java/re/jdk/6u11/promoted/fcs/b03/bundles/windows-i586/jre-6u11-fcs-bin-b03-windows-i586-p-10_nov_2008.exe)
then 6u12 b02 jre1.6.0_12-c.msi (copied from %APPDATA%) worked