java heap space eh? i will have to download the new version myself and see if it hits memory limit for me. generally speaking, java programs are launched with i think a 75MB heap space by default. presumably your computer has more than enough room for that, but just to be sure, are you running a really old computer? you can change the heap space java programs launch with but again, has to be through the command window. what version of windows are you on? i think in some you can go to start menu -> programs / all programs -> accessories -> command prompt.
typically this will start you at a window that says something like c:\users\Joe or something. move your yatzr program to that directory, and then to execute it, type:
java -Xmx800m <name of file including the .jar at the end>
this will start the program with a cap of 800m instead of 75m of ram and then you shouldn't have the program run out of memory. actually im running an old version of yatzrs (all i have on this pc) and its taking a crap ton of ram, i never noticed that... java can be VERY memory inefficient, especially if you aren't focused on that aspect. it might be that your computer is just running out of memory.
before you try the above, with the command prompt, just open your task manager (right click on your task bar at the bottom of your screen, and click start task manager). go to performance. it should show the amount of memory on the left side, under Physical Memory. what is the total, and what is the free? then, run yatzr's program. what is the free now as it starts to crap out? if the free is about 0, your computer may be running out of ram, maybe closing other stuff while you use his program will free up some ram. if its not near 0 (if its more than 100 or 200 or so), when his program dies, then you need to try why i posted above. that error you have means it ran out of ram, so its got to be one of these two things... computer running out of ram, or program running out of ram.
edit:
here is a link that might be able to help you get your command prompt open