Does the current user account (for the computer, not filemaker), have the needed access permissions to open this folder?
That doesn't really look like a correct file path for a windows system. There's no drive letter.
You may also need to first map a drive letter to that server or directly to the folder.
(I have an older system (before externally stored containers were possible) where the system just refers to drive letters x: and z: for some file/container actions. The client machines have mapped certain shared directories to those drive letters such that "X:" is the full file path to a specific directory. (And I have a script that runs a batch file to remap the drive letter should it get "lost" as happens from time to time in windows...)
Got it to work and now leads me to another question:
How do I create the directory if it does not exist?
Thanks for your previous response.
FileMaker 13 and older cannot create directories without using a plug in or a system script. (I've used export records to create and execute batchfiles to do this on windows systems in the past.)
I have read that a new script step in 14 can create new folders (if I understood the documentation correctly), but have not tried to use it. Get Directory is the script step, but upon further review, it may only allow the user to create a new folder in the dialog that this scripts step opens.
Either way, your client would need "write permission" access to the enclosing folder where you want to add a new folder.
Frankly, this looks like something that might be better managed with a container field set up to use external storage to a location on your server.