as suggested in the error message, increase the heap size by providing the commandline argument -Xmx along with the desired heap size to the java command.

edit the batch script starting the program to include that argument e.g. with -Xmx1024m and it should work just fine

I haven't ever used weka, but the message implies that you simply need a larger heap for Java. Try changing the 128m to 1G (or 1024m) for the Xmx value as Mr. Mauel has already mentioned. Note that it would likely also be beneficial to increase the starting heap size (-Xms )for performance, as this will avoid requiring (potentially multiple) heap expansions And if the Java processing is multi-threaded, you may need to increase the thread stack size (-Xss value). Note that large -Xss values will require an even larger -Xmx value... in which case you may need to experiment. If you are using 64-bit Java on a machijne with enough RAM, you can even makke the heap larger if required.