Hi Chris, welcome to the site.
You've got it trying to save the screenshots in a place where it doesn't have permission to do so. Just change the screenshot folder to a directory where you are allowed to save files. The default would normally be something like your Documents\DonationCoder\ScreenshotCaptor\Screenshots folder..
So oddly enough I just got this on my computer this morning too.
When I launched the app (which for some reason didn't launch on startup as configured) the app seemed to hang for quite some time (20-30 seconds) and then I was able to take a screenshot.
I'm currently running a slightly older version (4.31.2) (as i'm waiting for chocolatey to approve the install which is a whole other story!) and this is the first time I've seen this error message.
When I launched SC this morning all of my normal thumbnails are not showing up and the left screen is completely empty. When I went to File/Saving and loading, my screenshot folder is set to c:\andy\screenshots and not the location referenced in the error message (c:\program files(x86)\ScreenshotCaptor\screenshot - 20200214-113625.png)
If it makes any difference, my settings are stored in a redirected folder at \\servername\user$\myusername\My Documents\DonationCoder\ScreenshotCaptor\
I've had the funky empty screen folder show up occasionally and a restart fixes it (and did in this issue). I was also then able to take a screenshot and carry on as normal without the original error message posted above.