Reposting the solution that worked for me:
FIXED THE PROBLEM by trial and some of the things everyone else tried and found didn't work. At least the pesky (to say the least) HPIO error screen hasn't popped up for ten minutes. Other readers with the same problem, please try this and report back if it works for you
Finder >
Macintosh HD >
Library >
Printers >
hp >
hpio
drag hpio to trash
this required me to enter my admin. password
then
woosh! a happy sound I hope since this is the first time I actually wrote a message without the error box.
Also this just in from HP:
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hank you for contacting HP Total Care.
I understand you are looking for software for Leopard. At this time, HP only supports the preloaded driver install on Leopard.
The print only drivers (no scan features) are available (built-into OS 10.5). If you installed Leopard, you would need to go to Additional software and install the drivers for your HP printer. If your computer was purchased with OS 10.5 installed the drivers are already available. You should be able to plug the printer in and have basic functionality.
Refer to Apple document:
http://docs.info.apple.com/article.html?artnum=306684#hpdrivers
HP Engineers will be releasing an new version of the software for your printer, but it must be fully tested before we will release it for download. We have no ETA. You can sign up for updates on the hp.com web site and will be notified when the software is available. See link below.
HP's subscriber's choice is a free service where you can select to receive timely email notifications ranging from software and driver updates to creative ways to do more with your HP products.
http://h71036.www7.hp.com/hho/html/3618-0-0-225-121.html
NOTE: We have had a number of customer install the 9.5 drivers and have full functionality. HP does not guarantee this will work, but you are welcome to try it.
http://h10025.www1.hp.com/ewfrf/wc/softwareDownloadIndex?softwareitem=mp-53269-1 &lc=en&cc=us&dlc=en&product=439488&os=219&lang=en
If the software above does not work, you will have to be patient and wait until the full feature software is available. You can use the print only drivers to access the print functions.
I hope this answers your question. If you need further assistance, please reply to this message and we will be happy to assist you further.
Sincerely,
MYRNA
HP Total Care