Some audio or video files have been created in a way that f4x does not support. Unfortunately, this is independent of the file extension. An Mp3, for example, can be created in many different ways.
If your files are not supported by f4x you can convert them, e.g. with the freeware version of NCH Swich
As your files are encrypted with your password, existing transcripts cannot be opened when resetting the password.
Therefore, for security reasons, all existing transcripts are deleted when you reset your password. This is unfortunately a little inconvenient, but the safest option.
If an error occurs during processing, the quota will be booked back.