It crashed in a VM, & wouldn't enlarge in this copy of Win10 Pro, but, if you're optimistic by nature you *might* want to try it again tomorrow... the app establishes a connection to the company's server, and judging from the small size of the app -- AI apps for photo FX or manipulation tend to be huge -- it's possible the image is meant to be uploaded & enlarged online. They just might have been overwhelmed by the response from GOTD users, and their server(s) couldn't handle the load. I tried the sharpening option, and it did make a difference, though it hurt rather than helped the test image I tried.
AI PNG Enlarger Pro adds the program's folder, which holds the app itself in a single file. A new folder's also added to ProgramData, and a couple of tiny [1kb] files are added to Users\ [UserName]\ AppData\ Roaming. The registry just gets one new key for uninstalling the app.