BON failed to deobfuscate old mods (1.7.3 beta)

[Dereku]

I trying deobfuscate OptiFine for mc 1.7.3 beta, but get an error.

An error has occurred - give immibis this stack trace (which has been copied to the clipboard)

immibis.bon.ClassFormatException: Unable to load class
at immibis.bon.io.IOUtils.readClass(IOUtils.java:30)
at immibis.bon.io.DirLoader.loadFromDir(DirLoader.java:43)
at immibis.bon.io.DirLoader.loadFromDir(DirLoader.java:38)
at immibis.bon.io.DirLoader.loadClassesFromDirectory(DirLoader.java:25)
at immibis.bon.io.ClassCollectionFactory.loadClassCollection(ClassCollectionFactory.java:15)
at immibis.bon.gui.NewGUI$13.run(NewGUI.java:962)

Screenshot: https://www.dropbox.com/s/sz5o38mpfk4ovgd/17_06_2015-1434476793.png?dl=0