[RT-AC66U stock] Unable to access network share through backup programs

I have a WD drive attached to the AC66U and shared through the USB Application - Network Place (Samba) Share / Cloud Disk. Drive is accessible through on a variety of computers (through Win (10) Explorer) and phones on network and using whatever user names I have set up on the AC66U. I am able to add and delete files on this drive in such a manner.

However, when I try to set up a backup through EaseUS Todo or AOMEI Backupper, the login credentials are not accepted.

If I enable...

[RT-AC66U stock] Unable to access network share through backup programs