In response to my previous Java post, I got a DM on Twitter from another university student asking if I'd come across the above error before. Often I do, when I'm programming in a dazed stupor at 3am, and I've done this:
% javac Something.java % java Something.class
Instead of this:
% javac Something.java % java Something
The error can be caused by any number of factors, but 99% of the time it's because of this. Much hair ripping has resulted from it!
(It turns out this was the problem. Glad I could help ^^)