For some reason, there are some HP model printer drivers that cause problems with the Copy function of the CanoScan Toolbox. Because of this conflict, when Toolbox Copy function connects with the printer driver, which is what it is doing when you select it from the dropdown. There had been some updates to the Toolbox software that corrected the issue. However, then HP release some new drivers for some models that reinstated the issue.
So the first thing to try would be to download and install the most current version of Toolbox for your scanner model (ver. 184.108.40.206).
If the problem isn't corrected with that, then you won't be able to use the COPY function unless HP updates there printer driver to correct the issue. If you really must have the COPY option, then you might try using a older Toolbox just for that feature. If that is a consideration, then get the Toolbox ver 2.2.3 from the CanoScan N650U download page.
The COPY function from this version should work fine with the HP printers.