Problem solved. Without getting too technical the issue is when you are in the Finder on the Server the selected file locks when an image is opened. Clicking on a different file sometimes will unlock it, but this is a workaround that doesn't solve the problem. Apparently the "write access not granted" issue is a result of the Finder in Mojave, Photoshop CC, and the server not quite getting along with each other, which is why all your vendors will tell you that it isn't them it's the other guy. I am on a Synology Server DS916+ using SMB3 protocol and running Mojave 10.14.4. This worked for me. Go the View Menu in Finder and turn off ALL view options except the tool bar and the side bar containing your favorites. Restart the computer. You should now be able to open and save directly to your server. The Preview Panel seems to be the main problem. If you like you can turn on the other view options one at a time and see if the problem recurs. If so turn off that option. Also since the preview function seems problematic, you may want to set your Photoshop Preference for Save Preview to "Never." If you feel you are working blind because no preview images are available, that is what Bridge is for. Just view and open image files from Bridge instead of in the finder. Please let me know if this also works for you. In any event, if you do choose to work on your local disk there is no reason to copy and delete files. Use a synching app!! If you are on a Synology server their Cloud Station app does a great job, and is easy to use. ... View more

The short answer from Adobe is that they only support saving to a local disk. The issue appears to be that Photoshop perceives the file on the Server to be locked or in use. By far the easiest workaround is to use Bridge. From Bridge consistently use the shortcut menu with "Open With" and choose Photoshop. Do not use the "Open" function. Do not double click. Your file will now save to your server consistently. If you make a mistake you will need to deselect the folder you are opening from in the finder to release the lock on the file. Alternatively, if you have a Synology server, the Synology app "Cloud Station" will effortlessly synch local and server folders, and it is extremely easy to add or remove folders to synch as you need. I have no idea why using "Open With" from Bridge works, but it does. It therefore seems that Adobe could potentially solve this issue. My research indicates this is a Mac issue and goes back to at least 2011. At various times Adobe has maintained this is an Apple OS problem (pick which one), that they can't reproduce the issue on their servers, and then finally falls back on "we do not support saving to a server" due to blah, blah, blah. There is probably an incompatibility between some API utilized in Photoshop and Mac networking parameters. I surmise using Bridge as described bypasses this. Hope this helps. ... View more