it's always failed that use mount.cifs to mount a share from samba server which is in share mode by "security = share".
i checked the source code of cifs.ko found that it is because it didn't provide password in tree connect step.
if samba server is in user mode by "security = user". it is okay because authentication in done in session setup step. but in share mode, authentication is needed to be done in tree connect step, if there is no password passed to samba server. it is sure that client will failed to log on to samba server
Fixed in cifs-2.6.git on kernel.org will request mirror to mainline kernel for 2.6.16 kernel and will be in cifs 1.41 (or 1.40a)
Fix is also in svn on samba.org in linux-cifs-client/branches/linux-2.6-cifs-git-devel/