Comment 8 for bug 869842

If you have jre6 and later installed jre7, C:\Windows\System32\javaw.exe is java7.
Sikuli IDE uses it by default. So you need to tell Sikuli-IDE.exe to use proper path to java6.

You need rewrite batch files in Sikuli's install folder.

[Sikuli-IDE-w.bat]
@echo off

PATH=%PATH%;%~d0%~p0libs
set JAVA_EXE="%PROGRAMFILES%\Java\jre6\bin\javaw.exe"
if defined PROGRAMFILES(X86) set JAVA_EXE="%PROGRAMFILES(X86)%\Java\jre6\bin\javaw.exe"
start /B "Sikuli-IDE" %JAVA_EXE% -Xms64M -Xmx512M -Dfile.encoding=UTF-8 -Dpython.path="%~d0%~p0sikuli-script.jar/" -jar "%~d0%~p0sikuli-ide.jar" %*

[sikuli-script.bat]
@echo off

PATH=%PATH%;%~d0%~p0libs
set JAVA_EXE="%PROGRAMFILES%\Java\jre6\bin\java.exe"
if defined PROGRAMFILES(X86) set JAVA_EXE="%PROGRAMFILES(X86)%\Java\jre6\bin\java.exe"
%JAVA_EXE% -Xms64M -Xmx512M -Dfile.encoding=UTF-8 -jar "%~d0%~p0sikuli-script.jar" %*