Mac will connect to Windows or NAS file share via SMB

You need to tell the connection what TCP "port" you wish to connect to as well as the IP address. SMB connections usually would be done like this from the Finder "Go" menu command:

smb://xx.xx.xx.xx

where xx.xx.xx.xx is the IP address of the NAS device. For more info and a screen shot example take a look at:

How to connect with File Sharing on your Mac - Apple Support

Good luck...

You could try to use wireshark or some other network protocol analyzer to see what is happening exactly (you may need to get permission to use a tool like this on a network that you don't own). Are you certain you have the correct IP address of the SMB server? Do other people connecting to this server have any problems? Do any others use Mac's? Perhaps try from another account on your mac (use the "Users & Groups" in System Preferences to create a new account). Are you sure the NAS is up and running correctly? What is the model and brand of NAS box? Have you tried to talking to the system admin person responsible for the NAS box or your network? When was the last time you successfully were able to login to the NAS box and what has changed since then?

Good luck...

The important info is contained in the packet contents which is part of the window below the list of packets (which is the part displayed above). From what I see above, the source IP address is 93.50... and the destination address is 192.168.1.103 and the first packet in red is of type 445 which is SMB.. so that would appear to be part of the reply from the 93.50... server to the 192.168.1.103 client?? You should highlight the packet 7 and then 8 and see what the contents show you... You might want to set up some filters to show only traffic between the NAS server and the client (your mac) so that you con more easily show just that information (busy networks make this sort of filtering crucial). I'm not good enough with SMB protocol but you seem pretty sharp and able to do a bit of research and see what is expected and what you end up getting. Might even want to do the same thing on the Mac that is working so you can see what a successful SMB connection looks like.

Good luck...

Doing this sort of network analysis is very difficult via these discussion forums. What I would recommend for you is to understand the SMB protocol and use wireshark to look at a successful SMB protocol exchange and then look at what is different in the SMB failing system.

With the filter suggestion I gave above (substitute the real IP address of the SMB server and the working Mac and then the failing mac) look for differences and similarities. You can save the contents of a session and have two instances of wireshark running on both the working SMB client as well as the failing client and then see where they diverge.

Do a little research on how the SMB protocol works in order to recognize the key packets from/to the server and the client. Perhaps you have a co-worker or friend who can help in person? Wish I could help more than give some suggestions, but this sort of thing can take a while, so be patient and learn as much as you can as you try and solve the problem.

Maybe look around on youtube for some video's that use wireshark to help solve smb problems?

Good luck...

Filter something like:

ip.src == 93.50.xx.xx or ip.dst ==93.50.xx.xx

where you put the real IP address of NAS server would get all the traffic from and to it. Might want a bit more restrictive filter if there are lots of systems with connections to NAS server.

(ip.src == 93.50.xx.xx and Ip.dst == 192.168.1.103) or (ip.dst ==93.50.xx.xx and ip.src == 192.168.1.103)

would get traffic between only the NAS server and the 192.1698.1.103 system

Good luck...

Found this YouTube explanation of using wireshark to diagnose an SMB problem...hope it helps

Detect SMB/SMB2 Errors with Wireshark - YouTube

And here is an example (high level) protocol exchange sequence:

Microsoft SMB Protocol Packet Exchange Scenario (Windows)

Good luck...

If it works fine from another Mac, then possibly the NAS server is setup to only allow certain computers as well as only certain users to access the system. Are you the admin person for the NAS server box? If not, then you should talk to that person and describe your problems and see if they have any suggestions.

Good luck...