DVD region prolem

I am developing a dvd compilation in delphi. Using delphi, ffmpeg, dvdauthor tools, mkosiso.
I succeeded with all parameters and dvd compilation, now I got a problem where the ISO that I produce works under programs such as vlc... unfortunately it doesn't work under windows media player (win7, WMP 11).

It reports a problem in the region that due to it -- it won't play the dvd.
I need to make it work properly under the wmp due to the fact that that is an indication to whether it would work for me properly under the car entertainment system that it was originally developed to work for.

To make the dvd ISO file, I use the dvdauthor tools for windows,. these tools had previously a couple of versions and I remember having the same exact problem once, and to solve it I simply replaced the dvdauthor tools to the latest version.... Unfortunately this isn't the case this time,. And I am using the latest version of the dvdauthor tools (as far as I check uptodate).

In addition, I have checked with .IFO viewer the regions that it suppose to support,. according to that alll regions are enabled, so as far as to the binary written output, there seems not to be any issue with these regions setting.

I believe that there are other switches or checks that the WMP, and car entertainment system does in order to check the validity of the dvd -- that I am missing....