It usually means the file was corrupted. In your case, this was probably caused by interrupting an update in the middle while the data was being written.
At least 2x per month is my recommendation.
You can update whenever you want. Some people update 5x per day. I recommend not updating that much but it is up to you.
It is very important to let the update finish.
Here is my general advice on running a system in an easy to maintain way.