Is it still possible to load the old 3DS-files from Autocad? To me it more sounds that your Architectural software had changed something in the export filter that Pro does not understand. It is such a pitty that there are already several variation of 3DS-files around that are not totally compatible. Example: 3DS-files from Cinema 4D always create an error message saying that the materials are not treated correctly. When i load up a 3DS from other 3D applications it is ok. My experience is, that it often has to do with materials/texturing. Maybe you contact the other software company and ask what they have changed. And what their proposition is to solve the problem. Are there other export options for 3D models? "obj" for example, or "lwo". You could try those too - if possible.

One day your ship comes in - but you're at the airport.