The last example in the "available" task documentation: <available property="have.extras" resource="extratasks.properties"> <classpath> <pathelement location="/usr/local/ant/extra.jar/> </classpath> </available> The definition of the pathelement's location does not have a closing double-quote.
Fixed in CVS HEAD; will merge to 1.6 branch in case of a 1.6.4 release shortly. Thanks!