Build fails - Because output file access is denied?

[SDWriterClmt]

This is with Flare 2018 on Windows 10. Very recent issue, started happening 'spontaneously' with one target in my project. Call it Project A. It has two HTML5 targets:
* Target A publishes to our server, a URL that has public access
* Target B publishes to our server, a URL with internal-only access for beta purposes

Targets A and B are identically configured. Only the publish destinations are different. Both targets build without issues -- until today. Now the internal version builds and publishes fine, but the public version fails instantly with the following error about not accessing the path to some multimedia file in the output. Any ideas on how to get around this? Delete the multimedia file? Blow away all my output files? I'm stumped.

The result when I try to build both targets:

Flare_build_error.png

And when I try to publish Target A, it skips publishing w/o trying to build. This is a new one on me:

Flare_build_error2.png

[SDWriterClmt]

Well.... I did find a difference between the two 'systems' though I cannot explain it. I decided to have a close look at that multimedia file, which appears in the output of both targets. Looking at the security permissions it's obvious that somehow, SOMEHOW, I lost Read/admin permissions for this particular Target-A file. WTH.

So it may not be a Flare issue? I guess my next step is to speak with tech support and get this file unlocked.

Flare_build_error3.png