The most common error i have seen, and the problem this FQA addresses is when you are sending a file to the TINI's flash, like the OS, or slush(or anything else in bank 7), it starts to send the file, but after a little while it says something like "TINI not responding!".
basically the problem seems to be that there is to much latency with the linux 2.4 serial implementaion on some machines, and javakit is expecting a reply faster than it gets it, and when it doesn't get the reply quick enough, it assumes that the TINI is no longer present. The first thing to try is 'setserial low_latency'. if that doesn't work you are going to need to pass some args to javakit it make wait longer for a reply. try telling it "-flushWait 300 -resetWait 300", if that doesn't work, increase those numbers untill it does work, if you cant get it to work no matter how high you set it, there may be a problem with your TINI.