Doh, that’s a pain.
Here’s some (messy) code to test a few things, see how you get on.
The calls to PathFileExists and GetFileAttributes will at least give you a human readable error message to let you know what the problem is. This will probably give you a insight into whats going wrong.
Xojo probably use these calls inside the framework, I don’t know which though. I’m guessing PathFileExists (due to the historic problems with getting info on network share from previous posts above), but they might have moved to GetFileAttributes recently which is why there might be a different result with different versions of Xojo. I know they were trying to speed up FolderItems a little while back (or maybe I dreamt that).
Try clicking “check” before you click open to see if things work out of the box.
You might need to click connect more than once as it’ll randomly return error 53 for some reason (not figured that out yet, only found one reference to it, people probably just try a few times).
Upon closing the connection it will remain active for a little while (not timed it, probably, 30-60 seconds) while things are disconnected, MS probably put that in to stop reconnect spam issues on large networks.
It’s all worked as expected on my lan here, connecting from Win10 to different Server 2012r2 boxes, shares, folders and files.
If they are running anything under Win 8 or Server 2012 then that will change how much of this works:
See Remarks on GetFileAttributes “If you call GetFileAttributes for a network share, the function fails, and GetLastError returns ERROR_BAD_NETPATH. You must specify a path to a subfolder on that share.” “In Windows 8 and Windows Server 2012, this function is supported by the following technologies.”
You might also want to check your username, you might need to specify “DOMAIN\administrator” as your username if they disable local admin in preference of domain admin.