idea_xena branch build failed after opening it in IDEA: cannot find JavacTool

I can't build "xena" branch via "ant build" ever since I opened the code in IDEA. looks like IDEA and ant build use the same SDK definition.
I don't have  "1.6.0_25 64-bit" anymore and I even set the IDEA SDK to be 1.6.0_26 in IDEA, but the command-line build still fails:



build:
     [java] Buildfile: C:\projects\idea_xena\build\gant.xml
     [java]
     [java] doGant:
     [java] home is not defined. Defaulting to C:\projects\idea_xena
     [java] out is not defined. Defaulting to C:\projects\idea_xena/out
     [java] default:
     [java] compile:
     [java] jdk16.home is not defined. Defaulting to C:\Program Files\Java\jdk1.6.0_26
     [java] jdkHome is not defined. Defaulting to C:\Program Files\Java\jdk1.6.0_26
     [java] Project SDK '1.6.0_25 64-bit' is not defined. Embedded javac will be used
     [java] ##teamcity[progressMessage 'Cleaning up sandbox folder']
...
...

     [java]     [javac] C:\projects\idea_xena\java\compiler\impl\src\com\intellij\compiler\impl\javaCompiler\api\CompAPIDriver.java:60: cann
ot find symbol
     [java]     [javac] symbol  : variable JavacTool
     [java]     [javac] location: class com.intellij.compiler.impl.javaCompiler.api.CompAPIDriver
     [java]     [javac]     JavaCompiler compiler = JavacTool.create(); //use current classloader
     [java]     [javac]                             ^
     [java]     [javac] C:\projects\idea_xena\java\compiler\impl\src\com\intellij\compiler\impl\javaCompiler\api\CompAPIDriver.java:74: cann
ot find symbol
     [java]     [javac] symbol  : class TaskListener
     [java]     [javac] location: class com.intellij.compiler.impl.javaCompiler.api.CompAPIDriver
     [java]     [javac]       ((JavacTask)task).setTaskListener(new TaskListener() {
     [java]     [javac]                                             ^
     [java]     [javac] C:\projects\idea_xena\java\compiler\impl\src\com\intellij\compiler\impl\javaCompiler\api\CompAPIDriver.java:74: cann
ot find symbol
     [java]     [javac] symbol  : class JavacTask
     [java]     [javac] location: class com.intellij.compiler.impl.javaCompiler.api.CompAPIDriver
     [java]     [javac]       ((JavacTask)task).setTaskListener(new TaskListener() {
     [java]     [javac]         ^
     [java]     [javac] C:\projects\idea_xena\java\compiler\impl\src\com\intellij\compiler\impl\javaCompiler\api\MyFileManager.java:218: can
not find symbol
     [java]     [javac] symbol  : class ListBuffer
     [java]     [javac] location: class com.intellij.compiler.impl.javaCompiler.api.MyFileManager
     [java]     [javac]     ListBuffer<File> files = new ListBuffer<File>();
     [java]     [javac]     ^
     [java]     [javac] C:\projects\idea_xena\java\compiler\impl\src\com\intellij\compiler\impl\javaCompiler\api\MyFileManager.java:218: can
not find symbol
     [java]     [javac] symbol  : class ListBuffer
     [java]     [javac] location: class com.intellij.compiler.impl.javaCompiler.api.MyFileManager
     [java]     [javac]     ListBuffer<File> files = new ListBuffer<File>();
     [java]     [javac]                                  ^
     [java]     [javac] Note: Some input files additionally use or override a deprecated API.
     [java]     [javac] Note: Some input files use unchecked or unsafe operations.
     [java]     [javac] Note: Recompile with -Xlint:unchecked for details.
     [java]     [javac] 8 errors
     [java]     [javac] 100 warnings
     [java]
     [java] BUILD FAILED
     [java] C:\projects\idea_xena\build\gant.xml:17: : Compile failed; see the compiler error output for details.