Hi,
I'm not entirely positive this is the exact problem, but based on the information above, please check the following:
Open the Start Menu (windows menu)
Click on 'Run'
Type in 'msconfig'
Click on the 'services' tab
Sort by name
Look for 'Windows Image Acquisition (WIA)'
Make sure it's ticked
Press Okay and reboot
Try printing
Other than that, make sure you have the latest version of Paint.NET, and run it with administrative rights (Windows might be blocking PDN's attempt to start the service?).