Thanks for the suggestions. I had trashed preferences and recycled to no avail.
I eventually had to download the Io Uninstaller and completely reinstall an earlier version of the Io software. It’s running fine now although I have not moved back up to the most recent drivers (I’m waiting until I finish the show I’m working on before I try that again).
I should mention, for anyone having a similar problem, that I am running OSX 10.39 and have not upgraded to Tiger yet. I don’t know if that could affect things.
Thanks again for the resposes.