I am sorry to say that I have the same problem, Script errors without end. I am new to MoI and would just love to get it running.
I tried every fix I found on this forum ... using the june version, checking registry permissions, killed all Virus/Spyware/Firewall protection, checked IE security settings, you name the lot, nothing worked :(

Here my observations, I'm not sure if this is really a permission problem. Some of the functions work, some not. If there is a system problem I would have expected that none of the scripts will work ??? Somehow it happens most of the time when points have to be selected to define something, but not always ...

A list of the commands I tried, I will shorten the error message (Script Error Line xx Column xx to LxxCxx)

Line -> Line : OK
Line -> Polyline :OK
Freeform -> Control Points : L42C3
Freeform -> Through Points : L42C3
Freeform -> Sketch : OK
Rectangle -> Corner : after selecting the 1st point, L37C1
Rectangle -> Center : after selecting the 1st point, L37C1
Rectangle -> 3 Points: after selecting the 1st point, L30C1
Polygon -> Center : OK
Polygon -> Edge : OK
Ploygon -> Star : after selecting the 2nd point, L3C1
Circles -> Center : after selecting the 1st point, L32C1
Circles -> Diameter & Circles 3 Points : OK

Somehow it seems to be related to the point selection, but as mentioned .. not always?

Hope my observation will help,

Cheers,
Rainer