Instances of this class are thrown by BCEL's class file verifier "JustIce" when a class file to verify does not pass the verification pass 3 because of a violation of a constraint that is usually only verified at run-time (pass 4). The Java Virtual Machine Specification, 2nd edition, states that certain constraints are usually verified at run-time for performance reasons (the verification of those constraints requires loading in and recursively verifying referenced classes) that conceptually belong to pass 3; to be precise, that conceptually belong to the data flow analysis of pass 3 (called pass 3b in JustIce). These are the checks necessary for resolution: Compare pages 142-143 ("4.9.1 The Verification Process") and pages 50-51 ("2.17.3 Linking: Verification, Preparation, and Resolution") of the above mentioned book.