JTS compilation with IBM jdk1.5 fails due to "Fatal Error: Unable to find package java.lang"

Compiler cannot find java.lang package in case of compiling with IBM JDK 1.5.

See the snippet of compilation output:
...
[java] com.hp.mwlabs.orbportability.orbspecific.jacorb.compile:
[java] [echo] Performing JacORB IDL compile
[java] [classpath-builder] Property 'build.jacorb.classpath' set to classpath ...
[java] [echo] Performing JacORB orb specific compile
[java] [javac] Compiling 11 source files to /mnt/hudson_workspace/workspace/jbossts-testsuite-matrix/jdk/ibm15/label/RHEL4_x86/trunk/ArjunaJTS/orbportability/orbspecific-build
[java] [javac] Fatal Error: Unable to find package java.lang in classpath or bootclasspath