How do I create new tasks? How do I use jar's M switch? If your source-tree directory structure does not match your package structure, Ant's heuristic won't work, and it will recompile classes that are up-to-date. This causes the problem that an old version of ant (1.5.x in this cause) will be used with a new version of the ant script file. http://dukesoftwaresolutions.com/ant-exec/ant-exec-shell-script.html
But why don't you use the "package" attribute?