Mounting CIFS share on Ubuntu

Many thanks for responding and the excellent explanation.. however I still have the same issue.. quick summary

I have a share called /Documents, it's setup for CIFS and the default access in Frontview is read/write access, and Automatically set permissions on new files and folders is set to true.

my user on the readynas is Jinder who is UID of 1004 and he is a member of users (GID 100)

this is what I have in fstab

//192.168.1.65/Documents /home/jinder/Documents cifs noauto,users,_netdev,credentials=/home/jinder/.smbcredentials,iocharset=utf8,uid=1004,gid=100,file_mode=0774,dir_mode=0775 0 0

in the credentials I have my user/password for the user Jinder on the readynas

I can create files so if I do a

'touch j'

that's fine I can also do a

'rm j'

no problem.. but if I do a

'mkdir k'

then I get a

'mkdir: cannot create directory `k': No space left on device'

'df -k .' shows

Filesystem 1K-blocks Used Available Use% Mounted on
//192.168.1.65/Documents 1457032640 871754528 585278112 60% /home/jinder/Documents

This is SO odd.. why can I do somethings but not others? Incidently my ubuntu user is jinder:jinder

any other things you can think of that I can do to bottom this out?