That's odd. I just downloaded the JavaMail 1.4 API and the package for SharedByteArrayInputStream is javax.mail.util. Are you using a previous version of the JavaMail API? Check your classpath and make sure that no unnecessary JAR files are included. Many application servers include the JavaMail API and may have a version that is not compatable with the version you are using.
java.lang.UnsupportedClassVersionError: com/mail/SendApp (Unsupported major.minor version 48.0)
This means that the JDK you are using is an earlier version than what the JavaMail API was compiled with. JavaMail 1.4 has been tested with Sun JDKs 1.4 and 1.5 (see the README.txt). What version of IBM's JDK are you using? What application server did you get j2ee.jar from? Does it contain any JavaMail classes? Sounds like your original problem was a conflict with the version in the j2ee.jar file and the JavaMail API you downloaded (if that is what happened).
I understand. I'm stuck at JDK 1.4 much of the time because my employer uses Weblogic 8.1. So you can't use JavaMail 1.4. It still sounds like the j2ee.jar you are using has JavaMail classes in it. What app server/version is it?
I don't have access to WAS and the IBM web site is a maze. Perhaps you should post a query in our Websphere forum stating that you are attempting to use the JavaMail API with WAS 5.0 and the problems you are having.