First, although I have now received close to two dozen emails confirming the problem with Drive Setup 1.2.4 reported last time, I have also received several messages from people who do not have the problem. So it does not affect everyone. One person who did not have this problem was Theo Maschas, who found that the driver update not only worked fine but surprisingly fixed an odd problem where his Mac would not sleep when the Epson 800 was his default printer.
For those that do have the problem, Dave Provine inquires whether Drive Setup's "Mount volume at startup" box (found in Customize Volumes) might get incorrectly de-checked upon updating the driver. If so, it could cause the blinking question mark at startup. Dave says that this has been known to happen with older versions of Drive Setup. To fix it, run Drive Setup again, making sure that this option is checked.
In any case, I have received word from Apple that they are investigating this situation. Those that reported the problem to me have already been contacted by Apple. Dave Holzer, of Apple, also wrote me to say: "We are in the process of removing 1.2.4 from the internet site based on this information from MacFixIt." (MacInTouch reported this morning that it was already gone.)
Finally, in a somewhat related matter, Philip Gray reports that he cannot get Drive Setup 1.2.2 or 1.2.4 to even launch on his PowerPC based WGS9150/120.