In previous versions of DIRSIG (prior to 4.7), the "usemtl" assignments in a OBJ file were expected to be integer IDs because DIRSIG 4.6.x and early only supported numeric IDs. Some users discovered that the input reader would strip off a numeric part of an alphanumeric material ID. For example: "usemtl 1010_texture0.jpg" would just be read as "1010" and an entry with "ID = 1010" would be searched for in the material database.
In 4.7, we added the option to let material IDs (now referred to "labels") be alphanumeric. Hence, "usemtl 1010_texture0.jpg" is now a completely valid label and unless the material database was updated to read "ID = 1010_texture0.jpg" (when it used to be simply "ID = 1010") it will fail.
If you have scenes that took advantage of this hidden feature of the OBJ material assignment, then you will need to:
(1) Update the "usemtl" entries in your OBJ to match your material file exactly,
(2) Update your material file to match your OBJ "usemtl" entries exactly,
(3) Use the "<assign>" options in the GLIST to remap the OBJ labels to DIRSIG material labels.
Note that some of the standard scenes (for example, the "refinery" scene) utilized some of these assignment names in earlier releases of DIRSIG.