Further to my advice above. My drives were mapped but I went back network folder. But I still couldn’t access the NAS through there even though the mapped drives worked. Taking a look at the credential manager, I found the mapped credentials were using the NAS IP address and not the NAS name. And when looking at those credentials, I found the details were my pc name \ my nas user name.
e.g: simon_pc\nasadmin44
In the past i just typed my nas user name and the password and it worked fine, but something has changed. Anyhow, hope that this is not confusing and makes sense and helps someone else.