Cause: Paths were absolute (C:\Users\...) instead of relative.
Fix: Use the Asset Tracking tool in 3ds Max (Shift+T) to relink textures manually.

First, let's address the root cause. Unlike universal formats like .OBJ or .FBX, Autodesk’s native .MAX file format is backward incompatible.

This is a deliberate design choice by Autodesk to encourage upgrades. When a file is saved in a newer version, it may contain scene data, modifiers, or render elements that simply don't exist in the older code base.

This is the real-world solution for most users. You cannot convert a native .MAX file online directly, but you can convert a newer .MAX file into an older-compatible .FBX, .OBJ, or .3DS using a free online converter. Then you import that into your older 3ds Max.

How it works:

Important: You lose native modifiers, layers, lighting setups, and animation controllers. But geometry, UVs, textures, and basic transforms remain intact. For 70% of users (especially model buyers and freelancers), this is perfectly sufficient.