Windows Vista and 7 users with UAC enabled may often encounter an "Error saving hash data: Access is denied" message if they haven't given ApexDC++ the correct privileges to run. This is extremely easy to solve: Right click on ApexDC++'s exe file or shortcut. This can be found on the desktop or Start > Programs > ApexDC++.
Select Properties
Navigate to the Compatibility menu item (see attached screenshot)
Select Run as administrator
Restart ApexDC++
Once the program has finished hashing your files, it can successfully save the hash data to the Program Files directory.