Well ... some (much) tests later:

Other $ (hidden) shares work - KIX has no problem when called from such a share.

But: My development share was set up like this:
\\server\share$\netlogon\adlogin\adlogin_kix\kix32.exe

with no (list) access to share$, but read to netlogon and below.

I granted read for one user to share$ (like on the other $ share had I created before for testing), and the ADO query runs for this user !

So, the result seems to be as follows:

On Win7-64 (didn't test any other Win7 systems), when the user has no (list) access to the root directory of a share where the KI32.EXE is hosted in a directory below, some ADO query components - namely $objRootDSE.Get("defaultNamingContext"), fails.

Huh ?

Andy