Obviously if the file was moved or located on a separate volume, that would need to be resolved to fix this error. To do that, you would click the Resolve File Path option and re-locate where the file is on your machine. Doing so would let Stacher know where you're storing the file and can continue to track it in the library.
But, what if your file is corrupted??
You may not be completely out of luck. I'm working on a set of features that will allow you to take certain actions on media files. For example, file format conversion or in this case, repair corrupted files.
These are in Beta, but you can actually try them out right now! If you Shift+Click the menu under the media player, you will get some added options with the "Beta" badge next to them.
One of those options: "Attempt to Repair File". Now, I can't promise this will always repair all corrupted files, but it may be worth a shot if you otherwise feel out of luck.
When you select any of the Beta options, you'll notice the menu close and a spinner/loader will be in it's place. Wait for the loader to finish and the menu icon to return to normal. For media with a very long duration, this could take some time. If it was successful in repairing your content, it should start playing immediately when it's ready (assuming you didn't prematurely close the player). If the spinner stops and the media doesn't start playing, then the repair failed.
I know this interaction is a bit weird at the moment and there is no real indication of progress complete, but it is a beta feature.
If you do this, please take note that your original corrupted file does not get replaced. Instead, a repaired version of the file is created on your hard disk alongside the corrupted version. If hard disk space is a concern, you may want to manually delete the original corrupted file.
This feature, along with the other beta options in this menu, relies heavily on ffmpeg. Make sure you have it properly installed on your system if you would like to use any of these options.