Hey, guys - putting this here in hopes that someone here has updated (I haven't) and has Netherworks' Thumbnail Designer and can verify this and maybe have some thoughts as to how to fix it, before I try to contact Joe.
Got a report from someone that they are using Thumbnail Designer on a MAC. It worked fine in PP 11.2 but is NOT working in PP 11.3. They also note that they don't have a "Drive D" which is being called out.
I just checked mine Alisa, and it opens fine, so probably working fine. I, however, am on Windows 10 Pro, so not sure what the latest Mac OS is doing to cause that.