Click the button that says Show in Explorer. Once that opens showing you the file close LR and Delete it. Maybe restart your computer and LR and see if it is still there.
it WOULD (possibly) make life simpler if I could actually USE HF from Lightroom....the Last message says "Info.lua: bad header in precompiled chunk"
That error message likely indicates you've got a corrupted download. You might re-download and reinstall the software.
OK, I got the plugin to go away. Unfortunately, re-installing it from Helicon Focus (which is the only way I know of to get it installed) results in exactly the same errors... I even uninstalled and re-installed Helicon (which always seems like that old definition of insanity - doing the same thing over and over and expecting different results), with exactly the same result...
I've posted in the Helicon forum. Hopefully, I'll get a quick resolution 'cause it's a major pain in the *** to have to wade through thousands of images in HF trying to find the right stack to load...
"I've posted in the Helicon forum."
That's likely your best route at this point. That error message indicates a plugin file is in invalid format, and given you downloaded it twice, it's very unlikely that it got corrupted in the download/install process. So it's more likely that the server copy is invalid, something only Helicon can fix.