Make sure that the path to the javac tool is defined in the system classpath or in Preferences > Compiler. For example, on Windows, such a path could be C:\Program Files\Java\jdk1.5.0_03\bin\javac.
The preferences are located in various places depending on the operating system:
~/Library/Preferences/org.antlr.works.plistregedit.exe and browse the entries under HKEY_CURRENT_USER\Software\JavaSoft\Prefs\org\antlr\worksIn Windows Vista, if you are getting an error or a time-out when trying to debug, it is possible that port 49153 (which is the default debug port used by ANTLRWorks) is already used by another application. There are two ways to solve this issue: