I have I think a similar issue and just posted it..I can share with you the things I tried maybe something I did can help you.
Things I have tried - In no specific order
- Enabled Netbios on hardwired PC
- Pinged device while I cannot connect (with success)
- Connected to the NAS using the IP address in a browser and logged in as admin or my user
- Changed DHCP to the devices IP address
- Checked firmware version on the NAS drive
- Disabled AV program
- Checked firewall
Short term solution (I hope)
To connect to the NAS, All I have to do is reboot any of the 3 PC's and I can get access to the NAS. As an fyi - I use this NAS as a media server and use Apple TV to connect and get content and have never had any issues what so ever.
Here is the error message I get. The troubleshooter never finds an issue
Good luck