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This is a known issue with Mac OS X Mavericks and HP Scan. Unfortunately, there are no solutions to this problem yet. You will have to wait until HP or Apple release an update or fix.
Meantime, you can use other methods to scan to your Mac. You can use Apple's Image Capture application or Preview application to scan.
Open Image Capture application from there and that should allow you to scan. You can also scan using Preview application. Open Preview application, click File > Import from Scanner.
If you can preview the scan in HP Scan, then have you tried printing from there to PDF (Print to PDF) method ? That should also work.
I know this is not the answer you are looking, but unfortunately there is no direct solution. Please don't rate me Bad or Poor if you are not satisfied.
If you have any questions, please don't hesitate to ask as I'm happy to continue to help you.