It may be a number of things, but I would try to restructure your command with the options first, then the share path with the mount point as the final arguments (this matches the examples given in the documentation).
I would also suggest not using a dot file for your credentials, as they are actually a bug and not a feature.
sudo mount -t cifs -o credentials=/home/user/smb.creds //192.168.50.1/sharename /mnt/asus/