Not sure. First, can you check if you have mail.jar in your classpath. If it was already there, then can you list out all the jar files you have in your classpath. This class, should be in mail.jar usually.
You might look through each of those jars to see if any of them also contain the com.sun.mail.util.SharedByteArrayInputStream class. I haven’t encountered it with this particular class but I’ve run into class conflicts before where one jar has one version of stuff and another jar has another version.