That screenshot didn't come through. It's hard to say what happening without it... but...

Have you checked in your /Volumes folder to see if your casper share is listed even if it's not actually mounted?

This has happened to me a few times, I've had to remove the folder out of volumes. Umount wouldn't work because it wasn't actually mounted.

@kyoung You need to add your screenshot as an attachment to your post by dragging it into the section below the text field that says "Attach Images" We can't see it as a link.
Without seeing it, I can make a guess that you may have a leftover 'CasperShare' sharepoint stuck on your Mac that Casper Admin is seeing and therefore won't remount the share. That's one of the common reasons it doesn't work, but I'm only taking a shot in the dark since you didn't describe the issue and we can't see your image here.

Edit: Ok, better. I can see the image now. Yes, as @hkabik and I have both said, you probably have a share already mounted or more likely a broken mount point and Casper Admin isn't so graceful at handling that unfortunately. See if you can see it in Terminal

ls -al /Volumes

Assuming all was working before and its just started getting this error a common easy fix will be to restart the iMac.

Sir. That did it. Your good looks and charm are only exceeded by your intelligence and whit. Thank you very much!

Since we are at this point...

Apple has defaulted to SMB for the last couple of OS's so I have been checking SMB whenever it shows up as a choice. Is that a bad idea?

We've been running purely on SMB for some time now, it's been going well enough. I can't speak to ElCap, but on Yosemite Apple's SMB3 stack still doesn't play perfectly with our Windows based file shares. There are "delays" in the mounting and reading of these volumes.

Casper Admin seems particularly sensitive to this, it will mount the volume then I assume it doesn't respond back in enough time so it will attempt to re-mount the volume. Of course the initial mount attempt works, causing the second attempt to fail and I end up with a message as posted in your screen shot. Causing me to have to eject the the volume and relaunch Casper Admin. This does not happen every time, but when it does it oddly works perfectly fine after the initial failure/eject/relaunch.

Where this really plagues me is on replications. I have 3 or so DPs that I have to click replicate, let it fail, eject the mounted volume (essentially same behavior as I stated above) and then try the replication again. It always works after the first failure/eject/re-replicate, and has just become part of my process of this point. I always have a finder window open to /Volumes when I am doing replications now.

I've tried all of the usual go to's (connect via IP, remove special characters from the casper share account passwords, etc) the behavior persists.

So long story short, yes I think SMB is the proper way to go. But at least in my experience it is not without bugs still.

Hi, I can't see the PNG, could you try posting again?

@hkabik - Same here with the SMB unmount (Win 2k). Changing to IP and getting rid of complex char's in the JSS passwords helped, but with 25 DP's worldwide, I now mostly have to use RSYNC to replicate.
We're still on 9.72, but what I've read doesn't give me hope that newer iterations will help.
JSS accounts are all AD accounts, FWIW.

Another odd thing I noticed in El Cap is that mounting SMB shares in the Finder (at least on this test Mac) requires the address to be smb://... and not SMB://... Had lots of those in the "Connect to Server..." box and they were not working. Drove me nuts.

@scottb

We're at 9.81 with a primarily 10.10 base at this point. All AD accounts as well. Issue has existed since at least 9.72 for us and still remains.