This is a long standing issue that has popped up since we started deploying Windows x64 edition on our new machines.
When joined to a Samba PDC, the XP x64 machine exhibits the following behavior:
Select a folder, go to security options and hit 'add' to add a
user. This brings up a dialog which reads:
"The program cannot open the required dialog box because it cannot
determine whether the computer named "server" is joined to a domain. Close
this message, and try again."
After which you see:
"Unable to display the user selection dialog. This action is only
valid for products that are currently installed."
This doesn't affect machines running Windows XP SP2 or Server 2003 XP1 32-bit editions. Their ACL editors work just as expected.
It only occurs when talking to a domain member Samba 3.0.X file server , but not when talking to shares exported by other machines joined to the same domain.
This is a known bug in 3.0.23 that was fixed in 3.0.23a. Can you please retry the current 3.0.23b?