The bit about the AlteredBush8aTL.tga didn't help, as that I have three of those in my Trees folder, just with a different prefix.
Don't worry about your age ... I'm not that far off. It all means nada ... ha ha
Anyway, only 1 alteredbush file will be the correct one. I would try disabling them all by putting a '-' at the beginning of the filename. I had a similar problem when I installed some new textures in my DBW 1.71. Suddenly a bunch of default maps wouldn't load anymore. Their load.ini's were pointing towards the #BDW tree folder instead of to the trees in the sfs files ... so I disabled the #DBW tree files with '-' and now the maps load again.
You could also edit the load.ini file and change the tree file to another texture, purely to see if the map will load ...
Tree0 = Trees\AlteredBush8a.tga
TreeLightMask = Trees\LightM256.tga
into for instance
Tree0 = Trees\dlv_MTO_AlteredBush8a.tga //AlteredBush8a.tga
TreeLightMask = Trees\LightM256.tga
or any other default tree file that you know is default.