This is a known problem. The limit for a text-message is 64Kb. Don't ask me why.
There's an easy workaround, use StreamMessage instead of TextMessage:
StreamMessage message = topicSession.createStreamMessage();
publisher = topicSession.createPublisher(topic);
Where 'msg' is a String containing the message you'd like to send.
i added some memory to jboss using -Xmx today, and it went through with no problem. the file is 2.6 mb to 3.5 mb. i believe much bigger text files can go thru if more memory is added using -Xmx.