TDW's program is very finicky about how an obj file is setup for import.
There's also the problem of files screwed up from early versions of his program.
Xerxes asked me about helping do a tutorial for SH4.
I'm thinking a good one about how to get obj files properly ready for import with S3D would be a good one.
So, Xerxes, send me the obj files you couldn't import from Blender so I can use those to do a tutorial.
Improper objs are also an issue with the GR2 importer by TDW and a lot of what applies to S3D, applies to TDW's importer.