Java APIs

I was using ant 1.5 with no problems until recently...then upgraded to 1.6 and had all sorts of problems so have gone back to 1.5. Now I get the error:

...unable to find a javac compiler:
com.sun.tools.javac.Main is not on the classpath.
Perhaps JAVA_HOME does not point to the JDK


(JAVA_HOME is correct) when trying to compile anything. I've read a ton of posts about this, all of which say to copy tools.jar into $ANT_HOME/lib - I've done that and still got the problem. Any ideas?

TIA