The error occurs because your web server of the source website does not allow a large number of read/write operations in a short period. Another possible reason could be that the file was deleted by some other program on your web server.

Also, make sure the server disk space of the source site is sufficient before you take a backup. In order to back up successfully, the amount of free disk space on the web server usually needs to be at least twice the size of the website.

So, please contact your web host to confirm these information. Then after they make relevant changes on the server side, you can try to take a backup again.