In addition to regular permissions, recent versions of macOS also support ACL’s (access control list). I don’t really know how to manipulate these, but I know that it is possible to do so in the Terminal.
I wasn’t aware that PhotoShop could create a resource file, but perhaps that is a feature I just didn’t know about. In my experience, resource files were created with a specialized program like ResEdit or Resourcerer. A resource file is kind of like a special type of folder that can contain other types of information inside it – photos, sounds, menus, code, etc. In fact, before OS X every application was a resource file. OS X introduced a new feature with a similar purpose, a bundle file. Bundles are more flexible than resource files, in fact a bundle is actually a folder with a special flag telling the Finder to handle the folder as if it was a file. So anything at all can be put in a bundle. Bundles eliminated the need for resource files, so they are no longer used in modern applications. However, support for resource files was still included up to 10.14, I think they are no longer supported in 10.15 since that was a 32 bit API.
I wonder if your Op Center Resources file is simply damaged? For example, if you transferred it to a USB stick formatted for Windows, then back to the Mac, the contents of the resource file would be lost. I think that might cause a disk error like you are seeing. That would happen on any version of macOS, not just Mojave.
That leaves the puzzle of why the resource file was there in the first place. If the database was opening this resource file, one would expect it to use it to display images, custom menus, or something similar. I’m surprised you can simply remove this line of code without impacting the operation of the database in any way. Perhaps the file now opens ok but a problem would show up if you tested all of the features of the database.