How to use Avisynth+AvsP with VirtualDub frame server?
Did you install the frameserver support with auxsetup.exe? You can test if it is working by trying to open your video.vdr with another instance of virtualdub.exe.

From your description it doesn't look you really need the frameserver. You can trim the video with avs itself (e.g. Trim(100,200)), this is more robust and efficient.

Btw did you know there is active avisynth community on forum.doom9.org, forum.videohelp.com