Can't mount Freecom NAS

I have searched the web and this forum many times for a suggestion of what has happened to my NAS access, but never found a solution despite trying many of the things suggested.

I have an external HDD (Freecom) which is sat on my home network with its own fixed IP address. On this drive I have a number of shares set up. One of which was created specifically for me to store Mac related stuff when I had my Powerbook back in 2006. I used to have no problem accessing this share from OS X Leopard (I know, it was a long time ago). Nothing has changed on the drive, but can I access it from my newer Mac (Macbook Pro, El Capitan)? No.

If I browse the network I see the drive, if I click on the drive I see the shares, then when I try and open the share, sometimes I am prompted for login credentials, sometimes I'm not, but the result is always the same: There was a problem connecting to the server "Freecom" Check the server name or IP address, and then try again. If you continue to have problems, contact your system administrator.

Perhaps I shouldn't be giving myself the credit for being the System Administrator, but that is the situation I am in, so where do I turn?

I can access the drive's web access page and create new shares, but these still can't be accessed. There are no permissions setable through the interface, in the past I always used guest access. It is a hugely frustrating situation that I wish someone was able to point to a possible root cause for.

I have dipped into the terminal world and created a nsmb.conf file in an effort to fix the problem, but I have limited experience there and can only work parrot fashion, not really understanding what I am doing.

If anyone can offer any guidance, I'd be very appreciative.

Thanks.