Hello, I know that error message is super frustrating. It basically tells you the file is "read-only," but since you've already checked and confirmed it isn't, you're left scratching your head. In Dynamics 365, that specific error is a generic catch-all. It means: "I tried to save my changes to this file, but something got in the way, so I'm just going to blame 'read-only' because I don't know the real reason."
Since your file isn't actually read-only, here is what is actually happening, ranked from most likely to least likely, and how to fix it.
1. The "Stale Cache" Problem (Most Likely)
Visual Studio and D365 keep a hidden "cache" of all the metadata (the descriptions of all your forms, tables, and classes) so the IDE runs faster. Sometimes, this cache gets corrupted or out of sync. When the compiler tries to write to it, it fails and throws that "read-only" error.
Close Visual Studio completely.
Open File Explorer and go to your PackagesLocalDirectory (usually K:\AosService\PackagesLocalDirectory or J:\...).
Find the folder for the model that owns that file (e.g., ApplicationSuite or your custom model).
Go into the bin folder inside that model.
Delete the .md files inside that bin folder. (Don't worry, these are just compiled metadata cache files; they will rebuild themselves).
Also, clear your local VS cache: Go to %localappdata%\Microsoft\VisualStudio\ and delete the XppCache folder.
Restart Visual Studio and do a Full Build on that specific model.
2. The "Invisible Lock" Problem
Even if the file property says "not read-only," a background process might have it "open" in the background. This prevents Visual Studio from writing to it.
Is GitHub Copilot running? I see it in your screenshot. Sometimes AI extensions scan files in the background and lock them. Try disabling it temporarily.
Is OneDrive or a backup software running? If your project folder is synced to the cloud, the sync engine might lock the file for a split second, causing the build to fail.
