Fst 2.57 java.lang.ClassNotFoundException on reading

[trixprod]

In some cases, i got this error :
stack_trace: java.lang.ClassNotFoundException: at java.lang.Class.forName0(Class.java) at java.lang.Class.forName(Class.java:398) at org.nustaq.serialization.FSTClazzNameRegistry.classForName(FSTClazzNameRegistry.java:197) ... 110 common frames omitted Wrapped by: java.lang.RuntimeException: class not found CLASSNAME: loader:jdk.internal.loader.ClassLoaders$AppClassLoader@67424e82 at org.nustaq.serialization.FSTClazzNameRegistry.classForName(FSTClazzNameRegistry.java:235) at org.nustaq.serialization.FSTClazzNameRegistry.classForName(FSTClazzNameRegistry.java:190) at org.nustaq.serialization.FSTClazzNameRegistry.decodeClass(FSTClazzNameRegistry.java:173) at org.nustaq.serialization.coders.FSTStreamDecoder.readClass(FSTStreamDecoder.java:478) at org.nustaq.serialization.FSTObjectInput.readClass(FSTObjectInput.java:939)
What would cause that ?