My Veeam Backup was working fine until one day I got this error:
Error: Client error: ChannelError: ConnectionReset
I was having this error for every backup job(new and old) and restore job. The configuration is: Windows Server 2008 R2 as vCenter and Veeam Backup Server and 2 ESXi hosts on a shared NAS.
Since it took me some hours to solve this issue the real problem was that on that server I have installed Symantec System Recovery (Symantec Backup Exec produce the same problem) and on that day I have uninstalled it. It seems that Veeam and Symantec are using some shared files/services so by uninstalling the Symantec it breaks the Veeam configuration.
Since the error explanation point on "Network issue" the solution is to run these 2 files: VeeamTransport.msi, vPowerNFS.msi and repair the installation. You can find them on this path: C:\Program Files\Veeam\Backup and Replication\Backup\Packages