I had this problem when I tried to use subversion on CIFS mounted NFS. I often got svn: Can't open file '.svn/myfile.tmp': Permission denied or svn: Can't create directory ... kind of error. After I used nounix the problem seems to be gone.

nounix: Disable the CIFS Unix Extensions for this mount. This can be useful in order to turn off multiple settings at once. This includes POSIX acls, POSIX locks, POSIX paths, symlink support and retrieving uids/gids/mode from the server. This can also be useful to work around a bug in a server that supports Unix Extensions.

Works for:

newer Debian, Ubuntu, CentOS distros.
Linux distros with CIFS support

> mount -t cifs //my.host/mydir  -o rw,nounix,user=,password= /mnt/samba