2013 back up to OSX 10.8/10.9 file server?

Acronis Home 2013 version 6514 (latest release).

I used to do network backups of my PCs using a boot CD to Linux SMB servers, but I'm moving to OSX file servers, and Acronis won't authenticate to the file server.

When I browse for location, I can see the server, I can click on it, but then I get an "Authentication Settings" window, which won't accept my (known good) credentials with a "Connection Failed, please verify user name and password" popup.

Same results on a 10.9 file server, doesn't matter if "allow guest users to access this share" is on or off.

I can use the same credentials when the machine in question boots to Win7x64 Ultimate to read and write files on that same OSX Share.

Is this something I should be able to do? I know OSX wasn't supporting SMB2, but 10.9 does, and it still doesn't work...

Thanks in advance for any hints as to how to make this work!