This looks like you have probably have conflicting jar files in your userlib exposing the same classes, but those classes are not compatible.
Have you upgraded to Email Connector from Email Template for example, and not cleaned out your application's userlib?
I would suggest going into the userlib folder and removing all duplicates you can find, keeping just the versions with the highest revision numbers in the filenames. Also, remove any .jar that are from old modules that are no longer in use.
Good luck!
Hi,
check if you have jakarta.activation-2.0.1.jar in lib folder and clean up your deployment folder
Hi,
I had the same issue, it was conflict between email template module and latest version of email connector.
I just remove the email template module and javax.mail jar file from user-lib.