1. Here's why
Freezes and crashes may occur if your Scene is 'too complex' and your hardware isn't powerful enough and/or lacks available System Memory and Virtual Memory.
'Too complex' refers to the following variables:
|A: The number of different models you've added to the Scene.|
|B: The 3D Points number in the top right corner of Build Mode.|
|C: The number and resolution of textures/materials.|
|D: The Movie/Photo Effects you're using.|
|E: How many Reflection Planes you've added in the Reflection Effect.|
|F: How many Spotlights that are set to Shadows: Dynamic in the Scene.|
|G: How many Spotlights you've selected in the Global Illumination Effect.|
1.1: To prevent your PC from becoming unresponsive when you start rendering a Clip or a Photo, you should try to reduce the number of all of the above, in particular E, F and G.
1.2: In addition, please increase the amount of Virtual Memory in Windows:
Knowledge Base article: How do you change the amount of virtual memory in Windows?
1.3: Alternatively, you could consider upgrading your hardware:
Knowledge Base: What kind of computer does Lumion need?
Knowledge Base: Which graphics card do you need?