Argument Out Of Range Exception in MechJeb Ascent Guidance

[Fadamor]

I was trying to use Ascent Guidance (Primer Vector Guidance model) for a high-altitude probe mission around Kerbin and the following error popped up as soon as I enabled the autopilot and while Guidance Status was still INITIALIZING:

LAST FAILURE: Uncaught exception (ArgumentOutOfRangeException): Index was out of range. Must be non-negative and less than the size of the collection. Parameter Name: Index.

Here are my inputs:

Periapsis: 46211.055 km
Apoapsis: 56938.156 km
Attach Altitude (checked): 90 km
Orbit Inclination: 113°
Booster Pitch Start: 100 m/s
Force Roll (checked): Climb: 113° Turn: 113° Alt: 75m
Stop at Stage #: 3
Auto-Deploy Solar Panels unchecked
Auto-Deploy Antennas unchecked

This mission had a LAN specification as well and I originally tried using a Launch to LAN setting of 229.2° when I got the error message above. I then tried the same settings without using Launch to LAN and the result was identical so I don't think Launch to LAN is involved with the error.