Hi,
this is a typical error which comes out when SnapDrive is not configfured correctly, as per the Administration Guide and therefore is not fulfilling all requirements.
I suggest you read the requirements in our documentation.
Additionally, if you navigate to the SnapDrive installation folder on your windows hard disk, then open the SnapDrvdbg.log just after the error occured, scroll all the way down, then read backwards: you will see that there even a link to a KB which explains how to tackle this kind of problems.
Most likely this is a name resolution issue between SnapDrive server and the source and/or destination storage system ,but could also be that you are not using correct credentials, as the error message suggests.
In fact RPC transport Protocol Setting is more demanding than just using http, you may want to setup SnapDrive to use http, instead. RPC requires cifs service to be running on storage system and that you setup SnapDrive service to run with a user which can be authenticated on storage system (locally, if it's a workgroup or through Kerberos, if both Storage and Windows are in the same domain).
In other words, it's easier to configure SnapDrive with http, as you just need to setup one (admin) user on the storage system and configure SnapDrive with that user and password.
I hope that helps,
Domenico Di Mauro