Hi Shapley,
Repairing the disk permissions can be done as following:
1. Open the the Applications folder.
2. Go to the Utilities folder.
3. Double-click on Disk Utility.
4. Select the hard drive containing the boot volume.
5. Go to the First Aid tab and select Repair Disk Permissions.
Note: This process may take several minutes depending on the Mac and amount of permissions that need to be repaired. The Progress Log will indicate when the process has been completed.
Next reboot your Mac and try plugging the USB again.
If the same persist, a such may also happen due to a conflict with the HP Smart Install feature which is Windows Based only and being wrongly read by the Mac, in order to resolve a such a Windows based PC will be required. any laptop should meet the purpose, the printer will be installed automatically by connecting the USB.
Next update and install the latest firmware below:
http://h10025.www1.hp.com/ewfrf/wc/softwareDownloadIndex?softwareitem=bi-115794- 2&cc=us&dlc=en&lc=en&os=4158&product=4110396&sw_lang=
Next follow the HP Smart Install Control Utility below: Select the Printer and follow the on-screen steps to disable the feature for the printer.
http://h10025.www1.hp.com/ewfrf/wc/softwareDownloadIndex?softwareitem=lj-129224- 1&cc=us&dlc=en&lc=en&os=4158&product=4110396&sw_lang=
NOw plug the USB back to your Mac and check for any difference
Please let me know of any change,
Shlomi