I had exactly the same problem. No of the suggested 'self help' solutions worked for me , ref. :
https://forums.stardock.com/486084/fences-support-faq
What *DID* work for me were to download version 3.10 from my Downloads at my Stardock account ( https://store.stardock.com/myaccount/products ) and then install that on top of what was already installed (I installed the version 3.10)
The way I comprehend it , then Stardock messed up somehow, either they made something that introduced a problem, or they offered us an update that we were not entitled to so that product did not work correctly after install because of too old product key or something.
Anyway , as written then just download and install 3.10 (or what is your correct version via your account download !).
P.S. :
It appears as if some people have issues with 3.10 (3,1,0,5 is the version installed on my system) , ref. :
https://forums.stardock.com/505007/page/1/
If your issue persists then solution appear to be to uninstall v. 3.10 and reinstall v. 3.09 .
(I personally do *NOT* have 'WallPaper Engine' installed so my issue with Fences has nothing to do with that !)