Solution

Add xalan.jar to the CLASSPATH includes for the s1as-deploytool process of install_dir/lib/processLauncher.xml; for example:

includes="appserv-assemblytool.jar,activation.jar,appserv-admin.jar,
appserv-cmp.jar,appserv-rt.jar,j2ee.jar,jaxrpc-impl.jar,appserv-ext.jar,
deployhelp.jar,admin-cli.jar,dom.jar,xercesImpl.jar, xalan.jar"