I found a very helpful site that solved my problem. I want to share it here for future reference:
In Kodi try:
Add network location > Protocol = Windows SMB > Server Name = IP address of the server PLUS then put :445 on the end (this is the SMB TCP Port Number) > OK
Eg > 192.168.1.1:445
Usernames and password may be required.
Then select the smb://ip.address.of.server from the list again to add your shares.
Source: HERE