SMBFS Mount suddenly stopped working. CIFS error

Answering my own question as I found the solution for my case.

It seems I suddenly needed to add workgroup to the parameters in fstab leaving the final code as following:

//172.22.64.50/Web/  /mnt/netapp smbfs username=*****,password=******,iocharset=utf8,workgroup=OUR-WORKGROUP,sec=ntlm  0  0