What causes the "Scan to computer is no longer activated" error message?
This is for Windows 10. Open task manager, go to Startup, scroll down to "scan to pc activation app", right click on Status "enabled", choose "disable", reboot...worked for me.
I have a HP Officejet Pro 8600 and one can disable Scan to Computer in the accompanying app: just click on the printer shortcut that was created during installation, go to Manage Scan to Computer, and then disable the feature and uncheck the Automatically start Scan to Computer when I log on to Windows box (in the picture below, I've already disabled this feature).
If you cannot find the shortcut: the app's default path should be "C:\Program Files\HP\printer name\Bin\".
This feature does not disable scanning from your computer - this works totally fine. It's only purpose is to to send a scanned document directly to the computer where this service is running when you scan at the printer - which is useless for me, personally.
I found the answer to this issue in the HP forums: https://h30434.www3.hp.com/t5/Scanning-Faxing-and-Copying/Scan-to-computer-is-no-longer-activated-again/td-p/3465249