Tascam Us-428 V. Panther.3.3, Getting it to work! Options

[British31]

I am at the end of my rope Here is the lowdown, I am running a Tascam US-428 on a 1ghz G4 with OSX 10.3.3 running the latest version of the driver 3.2.3 that I got off the Tascam DL site. Now at first, all is well, audio in, midi functions great, it is a veritable dream. 5 Mins later, all gone and I am in hell once more! No midi, no signal. I have a sneaking suspition that the audio midi setup panel is causing some grief as I attempted to work the unit on another drive with a fresh install. The unit works for sure as I set it up on an old mac G3 laptop and all was gravy. Any one else with the same problem? How can I fix it? Thanks