This could be a network issue. What kind of repository are you using? Did anything change like Firewalls, Antivirus,.. ?

Did the backup job itself complete successfully, as the log says nothing to process?

If you dive into your logs you should hopefully get some more information about the connection reset. Is your repository an SMB/NFS share or is it directly attached storage on Windows or Linux? Or even a dedupe appliance.

@regnor is spot on that this is a network communication issue and has given some great places to look. And upon re-reading his comment I realised he already asked what repository you’re using. But as I’ve listed them out I’ll leave it there.

This is most likely a firewall issue, something closing the connections prematurely, some firewalls can be very aggressive at port closure. Alternatively this could be something as simple as a lack of bandwidth between your gateway server and the SMB/CIFS share.

If you can give us a bit of a view of your backup infrastructure topology this would greatly help.

Thanks for the feedback. Backup job is linked to VMWare vct client. I will check the firewall rules or other network issue and let you know soon. Thanks to the Veeam Community members. You are the best. Since I am newbie Veeam user and have lot of questions but I always get support from the community. 

Chances are, the account that has access to the repository has expired and need to be renewed.

DNS lookup failures. ( workaround: identify the name and IP on which you want to communicate and then make a manual entry in the hosts file)

Additionally, check the account which has been used to configure vmware vcenter with VBR. If the user account fails on vcenter then too it will not allow to pass connections.