Field .PathUnit.m_vehicleTypes not found

Symptom

You may see errors such as:

System.IndexOutOfRangeException: Array index is out of range.
at OptionsMainPanel.AddUserMods () [0x00000] in :0

or

Field '.PathUnit.m_vehicleTypes' not found. [System.MissingFieldException]

Cause

You tried installing TM:PE on a pirated version of the game.

Solution

Buy the game.