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This is an error in their ReadMatMap.

The 3DS format has more capabilities than they import.. Change the function to this, and it will work:

private string ReadMatMap(BinaryReader reader, int size)

{
string cname = "";
while (size > 0) //search for A300
{
var id = this.ReadChunkId(reader);
int siz = this.ReadChunkSize(reader);

if (id == ChunkID.MAT_MAPFILE)
{
size -= 6;
cname = this.ReadString(reader);
size -= cname.Length + 1;
}
else
{
this.ReadData(reader, siz - 6);
size -= siz;
}
}
return cname;
}