I was getting the same vague error when I was trying to mount a drive (“An error occurred”) and finally got it working tonight. Here’s what I did, perhaps your situation is similar:
I was trying to mount one of the external USB hard drives I have connected to my Airport Extreme base station, I first launched the AirPort Utility app and selected the File Sharing tab under the Disks section. I confirmed that I had Enable File Sharing checked on and I had set the Secure Shared Disks config to “With a disk password”. When setting up the mount point in nitoTV, I had only entered a password, and left the user login blank, since I thought that was all I needed to access the hard drive connected to the base station. I’m pretty sure it was the blank user login that was causing the vague error.
I launched the Keychain Access app to see what was saved for the Airport Disk Password I had set and, sure enough, it had also saved my user name. So, when trying again to create the mount point in nitoTV, I made sure I had the following:
Mount Type - smb
Mount Address - .local
Requires Authentication - Yes
User Login -
Volume Path -
Actually, on my first try including the user login, I had the wrong password entered and I got an error message saying that permission was denied. But I was happy to see that error instead of the vague error I had been getting. I entered the correct password and it mounted just fine, although there was no notification that it had mounted. But when I went to nitoTV -> Files, I saw the drive mounted there.
You didn’t mention whether you were trying to mount a network drive (like me) or a shared folder on your computer, and you didn’t mention whether you’re running Windows or OS X on your computer, but I hope my experience is still helpful in some way.