When I open HP Scan Pro and attempt to scan a

The computer is looking for a "Twain" device. Although the printer is correctly installed, to scan a document or picture, you need a program to associate with the scanner and identify the "Twain" device. To do this, open up any photo software or even MS Paint. Under the File tab there should be an option to Import or Import from a device i.e. camera, scanner. This is the option you want. Select your HP Scan Pro as the Twain device and you can scan from your computer. The other way would be to open HP Imaging software package that came with the machine and configure your scanner from within the program. Either way works its just a matter of preference. Best of luck and reply back with any questions.