not instantiable

Hi everyone,
I'm customizing ODK for a specific purpose, every things went well even I've ran it as debug mode it worked well, forms submitted. But, when I generate it as signed apk, it crashes before launching and gives me this error:
Caused by: org.javarosa.core.util.externalizable.CannotCreateObjectException: not instantiable

I'm very confused :frowning:

Any help would be much appreciated!