I was having the same issue. Deleting the obj file fixed it for me.
C:\EpicGames\UE_5.5\Engine\Source\Programs\AutomationTool\Mutable\RunMutableCommandlet\obj
Sometimes, the obj folder in a project can cause problems because it holds temporary files that the system uses while building. If these files get messed up, locked by something else, or don’t match the current setup, it can create errors. By deleting the obj folder, you force the system to rebuild those files from scratch, which usually clears up any issues. It’s like hitting the reset button for the build process!