samba - Apr 2012 - Can mkdir on samba share but not copy directory from local disk to samba share

Hi

We are running a large samba servers within an NT4.0 domain (yes, I know)
The samba version is 3.5.10:
> smbd -b|less
> Build environment:
>    Built by:    root at sfw10-patch
>    Built on:    Wed Oct 26 11:23:15 PDT 2011
>    Built using: /ws/on10-tools/SUNWspro/SS12/bin/cc
>    Build host:  SunOS sfw10-patch 5.10 Generic sun4u sparc
SUNW,Sun-Fire-V210
>    SRCDIR:     
/sfw10/builds/build/sfw10-patch/usr/src/cmd/samba/samba-3.5.10/source3
>    BUILDDIR:   
/sfw10/builds/build/sfw10-patch/usr/src/cmd/samba/samba-3.5.10/source3
> (...)
running on Solaris (Sparc:)
> uname -a
> SunOS XXXXXX 5.10 Generic_147440-13 sun4u sparc SUNW,Sun-Fire-V440
File system is ZFS. The system has been recently moved from older
OS and samba versions. (I'm not the primary admin but the guy supposed to
know about the samba part.)
I've found now that since we moved there is trouble with some file
operations:

I can create directories on the share with mkdir (from Win XP) just fine,
but copying directories from a local file system to a samba share with
"xcopy ... /e" fails.
xcopy from samba share to samba share works, as well as xcopy'ing files.
Where should I start to dig?

Here's my configuration
> [global]
>         workgroup = YYYYY
>         netbios name = XXXXXXX
>         server string = Samba Server %v, Solaris 10 (ZFS)
>         security = DOMAIN
>         allow trusted domains = No
>         username level = 1
>         log level = 1
>         log file = /var/samba/log/clients/%m_%I
>         max log size = 512
>         load printers = No
>         printcap name = /dev/null
>         dns proxy = No
>         wins server = zzzzzzzzzzzzz
>         winbind trusted domains only = Yes
>         hosts allow = 137.248., 192.168.
>         nt acl support = No
>         printing = bsd
>         print command = lpr -r -P'%p' %s
>         lpq command = lpq -P'%p'
>         lprm command = lprm -P'%p' %j
> 
> [homes]
>         comment = Home Directories
>         read only = No
>         create mask = 0740
>         directory mask = 0750
>         veto files = /public_html/
>         hide files = /desktop.ini/
>         browseable = No
>         volume = HOME
> 
> [public_html]
>         comment = User Webspace
>         path = %H/public_html
>         read only = No
>         hide dot files = No
>         mangled names = No
> 
> [ntprofiles]
>         comment = Benutzerprofile
>         path = /WinNT-Profiles
>         read only = No
>         create mask = 0740
>         directory mask = 0750
>         hide files = /desktop.ini/
>         browseable = No
>         csc policy = disable
Kind regards
Wolfgang