After some days I revisited a project I have been working on for ages, and for some reasons it welcomed me with this error:

javax.faces.el.EvaluationException: java.lang.ClassFormatError: JVMCFRE113 unexpected EOF; class=de/mekos/MekosUtils, offset=0
at com.sun.faces.el.ValueBindingImpl.getValue(ValueBindingImpl.java:184)
at com.sun.faces.el.ValueBindingImpl.getValue(ValueBindingImpl.java:134)
at com.ibm.xsp.page.compiled.ExpressionEvaluatorImpl.getBindingValue(ExpressionEvaluatorImpl.java:151)

I have never seen that before, and there generally nothing wrong with the structure or similar. It's just a problem of elements not being signed with the expected ID. In this case the Java source file(s) had the "bad" signature, which - btw - is pretty able to access the server and execute code, just saying.

I'd have expected an error like "you are not allowed to... blablabla" but no, this is the different style to tell you so - so just sign your app with a "good" ID and everything goes back to normal.