still not working, i have found some hints. one at http://www.winscriptingsolutions.com/Articles/Index.cfm?ArticleID=7991&Key=Visual%20InterDev

Where it says :

You can set share permissions with WMI's Win32_Share, Win32_SecurityDescriptor, Win32_ACE, and Win32_Trustee classes

and also at :
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/netdir/adsi/iadssecurityutility_getsecuritydescriptor.asp

where it says some interesting things. It is mentioned that the accessmask which can normally be used to set what to retrieve (fileter on sacl, dacl, user or group information cannot be used on a fileshare. This would indicate that the secdescriptor for a fileshare is fundamentally different and probably needs a different way of interaction/syntax.
It also says you need to specify them parameters when setting the securitydescriptor of a fileshare. i have already tried several ways to get it to work but i am not secceedung nor can i find any example script on the net where fileshare ACLs are manipulated.

I think i am staring too long at the moment, so if anybody has a fresh idea..

regards,
MvdW