Hello David_Kelly, and welcome to the HP Forums, I hope you enjoy your experience!
I understand you are having issues with your printer assistant. I would love to try and help you, but I do need a little information first, such as which version of the 8600 you have. I am linking a few HP Support documents below that will show you how to find your product number. Also, please include which operating system you are using. Also, if you're using Windows, please include whether your operating system is 32-bit or 64-bit. With this information and the product number we can provide you with accurate information.
How Do I Find My Model Number or Product Number?
Mac OS X: How Do I Find Which Mac OS X Version Is on My Computer?
Which Windows operating system am I running?
Is the Windows Version on My Computer 32-bit or 64-bit?
In the meantime, I would suggest running this update: ftp://ftp.hp.com/pub/printers/sclitefileassociation/SCLiteFix_299026.exe
Good luck and please let me know the results of your troubleshooting steps. Thank you for posting on the HP Forums!