I have installed Screenshot Captor at two locations. Both locations use Redirected Folders to point My Documents, etc. to a server location. That said I experienced this same issue at both locations:

I have installed Screenshot Captor 4.8 from the regular setup exe on Windows 8.1 into the default location (Program Files (x86)\ScreenshotCaptor). After starting the program, I am presented with errors about not being able to move old screenshots. When quitting the program, it shortly shows an error balloon about not being able to save its settings to an UNC path, which is the network drive where the My Documents folder is located (\\server\share\DonationCoder\ScreenshotCaptor).

The solution that worked for me was manually adding the folders that make up this path: \\<server name>\RedirectedFolders\<user name>\My Documents\DonationCoder\ScreenshotCaptor\OLDER...

Thus I needed to add these three folders (see attachment):
1. DonationCoder
2. ScreenshotCaptor
3. OLDER

Hope this helps someone else!