Cannot be opened for writing errors after update to v3.04

Just upgraded and no matter what I try to change Mp3 says "cannot be opened for writing"

Even if I just click something to type to over where all the files are listed and don't change anything, when I click on another file Mp3 gives me the same message,

You will find a fair number of threads dealing with "cannot be opened for writing", e.g. this one:

Could you first use the search function and have a look a the existing threads and then, if the problem persists, tell us what you do and what you already tried to remedy the issue?