cannot update build.xml

Everytime i edit the build .xml of a DC , whose configuration has been imported from the DTR, build .xml doesnt get edited. Basically the DC gives the following errors while building:

1)Unable to find a javac compiler;

2)Perhaps JAVA_HOME does not point to the JDK

While my local webDynpro components can easily be deployed with the same NWDS on the Sneak Preview 2004 SP18.

Any clue???? In the build.xml i am giving the reference of javac.