I was having trouble with policies that install a package, because the client could not mount the distribution point. The distribution point is hosted on a Windows 2012 R2 server, just a folder shared via SMB. Created two local users: "jamfreadonly" and "jamfreadwrite". In Computer Management > File Share Distribution Points > File Sharing > Username field, I specified somthing like WINSERVER02jamfreadonly.

Casper Admin mounted the DP fine. So did Casper Imaging. And in Finder, Go > Connect to Server worked with the username in the form of WINSERVER02jamfreadonly.

In Terminal, when I ran the "sudo jamf policy -verbose", the errors included::

Result of the mount attempt: The URL to mount cannot be nil.
Result code of mount attempt: 10

I tried using the jamfreadwrite credentials just as a test, and didn't get different results.

In Computer Management > File Share Distribution Points > File Sharing > Username I tried removing the "WINSERVER02" from the username, and just used the short name of the account, but that didn't work, but at least "sudo jamf policy -verbose" to install a package resulted in a different error:

Result of mount attempt: Authentication error
Result code of mount attempt: 80

However, when I specified the username with a semicolon instead of a backslash, it worked fine, like this:

WINSERVER02;jamfreadonly

If you run into a similar problem, and search for that error string, I hope you find article, and find it to be useful. If so, please let me know if you've experienced it as well.