multiAVCHD Motion Chapters issue.

[Sark]

I have no problem with multiAVCHD doing everything it should except when trying to create motion chapters. Towards the end of the encode I get the error box attached.
Does anybody know what this relates to. I'm guessing it's an avisynth issue?
I can create motion menus, and motion title thumbnails, so avisynth is installed just fine. I also believe I had this working way back but now it has decided to play up. multiAVCHD is on an offline Win 7 system, so it's not a Windows update issue.

If anyone has had this issue, or can give me a clue as to where I should be looking for a solution I would be very grateful.

sark