In the 1G one you have -Xms and -Mmx reversed; mx is the max.
Try increasing the PermGen space? How many classes are there?! It might be helpful to include the entire stack trace/build output to help pinpoint what's going wrong, and during what--I mean, I'm compiling a half-million line project without having to increase the memory settings, so something's probably configured wrong.
subject: Issue : [javac] java.lang.OutOfMemoryError: Java heap space