Not sufficient privileges for some items to access smb drive

I am sharing a drive using samba on my server...
when i try to write a file on this drivefrom a MAC I got this message:

"The operation cannot be completed because you do not have sufficient privileges for some items "

However i can browse this drive, i can read any file but no acces to write...

I checked my smb configuration and here is my smb.conf


[600GB]
comment = 600 GB Space
path = /mnt/nfs/600GB/users
read only = no
browseable = no
writable = yes
public = no
username = 600GB_smbshare



and we already assigned the right for everyone to access /mnt/nfs/600GB/users for everyone to R/W

Do you know how to solve it
Thank you

Dany

Is this a pc drive and you happen to have it formatted as ntfs?

Actually it's a linux drive formated as reiserfs...
many windows users and few Mac users are connected to this drive, however whe i tried to add this new user I got the previous message

Dany