That you are trying to upload a backup archive from your site to your NAS. The transfer is performed using FTP. Ask them if there are any blocks on outgoing connections.
Oh, while I was writing I remember one last check that you could do: can you please switch the flag about the Passive mode?
As a final note, please remember that home/small business NAS could create problems, since they can not handle the incoming stream of data. Moreover, the real bottleneck is the bandwidth of your home/office. If it's under heavy usage, the upload request could take so much that gets closed by the remote server.
So, long story short: you can try using your NAS, but we strongly suggest you to rely on cloud services like Dropbox or Amazon S3
Davide Tampellini
Developer and Support Staff
🇮🇹Italian: native 🇬🇧English: good • 🕐 My time zone is Europe / Rome (UTC +1)
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!