Here is an updated log after renaming enemy and searching for issues in the models.txt, level.txt and the billys1.txt to try and resolve the issue.
Total Ram: 4294967295 Bytes
Free Ram: 4262105088 Bytes
Used Ram: 2936832 Bytes
OpenBoR v3.0 Build 3742, Compile Date: Dec 7 2012
Game Selected: ./Paks/bor.pak
FileCaching System Init...... Enabled
Initializing video............
'data/video.txt' not found.
Initialized video............. 320x240 (Mode: 0, Depth: 8 Bit)
Loading menu.txt............. Done!
Loading fonts................ 1 2 3 4 Done!
Timer init................... Done!
Initialize Sound.............. Done!
Loading sprites.............. Done!
Loading level order.......... Done!
Loading script settings...... Done!
Loading scripts.............. Done!
Loading models...............
Cacheing 'Flash' from data/chars/misc/flash.txt
Cacheing 'Axel' from data/chars/Axel/Axel.txt
Cacheing 'Blaze' from data/chars/Blaze/blaze.txt
Cacheing 'Haggar' from data/chars/haggar/haggar.txt
Cacheing 'Guy' from data/chars/guy/guy.txt
Cacheing 'Cody' from data/chars/cody/cody.txt
Cacheing 'Carlos' from data/chars/carlos/carlos.txt
Cacheing 'Lucia' from data/chars/lucia/lucia.txt
Cacheing 'Jessica' from data/chars/Jessica/jessica.txt
Cacheing 'Adam' from data/chars/adamx/adamx.txt
Cacheing 'Skate' from data/chars/skate/skate.txt
Cacheing 'Sandwich' from data/chars/misc/bread.txt
Cacheing 'Barbecue' from data/chars/misc/meat.txt
Cacheing '1up' from data/chars/misc/1up.txt
Cacheing 'Money' from data/chars/misc/money.txt
Cacheing 'Glasses' from data/chars/misc/glasses.txt
Cacheing 'Radio' from data/chars/misc/radio.txt
Cacheing 'Emerald' from data/chars/misc/emer.txt
Cacheing 'Phone' from data/chars/misc/phone.txt
Cacheing 'Drum' from data/chars/misc/drum.txt
Cacheing 'Tires' from data/chars/misc/tires.txt
Cacheing 'Barrel' from data/chars/misc/barrel.txt
Cacheing 'Andore' from data/chars/andore/andore.txt
Cacheing 'Atlas' from data/chars/atlas/atlas.txt
Cacheing 'Billy' from data/chars/billy/billy.txt
Cacheing 'Black' from data/chars/black/black.txt
Cacheing 'BigBear' from data/chars/bigbear/bigbear.txt
Cacheing 'Callman' from data/chars/callman/callman.txt
Cacheing 'Dave' from data/chars/edi2/edi2.txt
Cacheing 'Dirk' from data/chars/dirk/dirk.txt
Cacheing 'Elic' from data/chars/elic/elic.txt
Cacheing 'G' from data/chars/g/g.txt
Cacheing 'Jade' from data/chars/jade/jade.txt
Cacheing 'Mic' from data/chars/mic/mic.txt
Cacheing 'MayLee' from data/chars/may/may2.txt
Cacheing 'May' from data/chars/may/may.txt
Cacheing 'Philippe' from data/chars/Philippe/Philippe.txt
Cacheing 'Sirou' from data/chars/sirou/sirou.txt
Cacheing 'thug3' from data/chars/thug3/thug3.txt
Cacheing 'Mary' from data/chars/mary/mary.txt
Cacheing 'zack' from data/chars/zack/zack.txt
Cacheing 'Wong_Wong' from data/chars/wongwong/wongwong.txt
Cacheing 'Barbon' from data/chars/barbon/barbon.txt
Cacheing 'billys1' from data/chars/billys1/billys1.txt
Cacheing 'Bigben' from data/chars/bigben/bigben.txt
Cacheing 'Knife' from data/chars/misc/knife.txt
Cacheing 'Shot' from data/chars/misc/shot.txt
Cacheing 'Heli' from data/chars/misc/heli.txt
Cacheing 'fight' from data/chars/misc/fight.txt
Loading 'Flash' from data/chars/misc/flash.txt
Loading 'Axel' from data/chars/Axel/Axel.txt
Loading 'Blaze' from data/chars/Blaze/blaze.txt
Loading 'Haggar' from data/chars/haggar/haggar.txt
Loading 'Guy' from data/chars/guy/guy.txt
Loading 'Cody' from data/chars/cody/cody.txt
Loading 'Carlos' from data/chars/carlos/carlos.txt
Loading 'Lucia' from data/chars/lucia/lucia.txt
Loading 'Jessica' from data/chars/Jessica/jessica.txt
Loading 'Adam' from data/chars/adamx/adamx.txt
Loading 'Sammy' from data/chars/skate/skate.txt
Loading models............... Done!
Object engine init........... Done!
Input init................... No Joystick(s) Found!
Done!
Level Loading: 'data/levels/sor/stage1a.txt'
Total Ram: 4294967295 Bytes
Free Ram: 4245925888 Bytes
Used Ram: 40706048 Bytes
Command 'xmin' not understood in file 'data/levels/sor/stage1a.txt'!
Command 'xmax' not understood in file 'data/levels/sor/stage1a.txt'!
Loading 'Phone' from data/chars/misc/phone.txt
Loading 'Sandwich' from data/chars/misc/bread.txt
Loading 'Drum' from data/chars/misc/drum.txt
Loading 'Knife' from data/chars/misc/knife.txt
Loading 'Tires' from data/chars/misc/tires.txt
Loading 'Barrel' from data/chars/misc/barrel.txt
Loading 'Radio' from data/chars/misc/radio.txt
Loading 'Zack' from data/chars/zack/zack.txt
WARNING: data/chars/bigben/bigben.txt tries to load a nonnumeric value at jumpframe, where a number is expected!
erroneus string: data/chars/bigben/jump.gif
Loading 'Bigben' from data/chars/bigben/bigben.txt
********** An Error Occurred **********
* Shutting Down *
Fatal: No cache entry for 'billys1' within 'data/levels/sor/stage1a.txt'
Total Ram: 4294967295 Bytes
Free Ram: 4245397504 Bytes
Used Ram: 41496576 Bytes
Release level data...........Level Unloading: 'data/levels/sor/stage1a.txt'
Total Ram: 4294967295 Bytes
Free Ram: 4249165824 Bytes
Used Ram: 37773312 Bytes
Done.
Total Ram: 4294967295 Bytes
Free Ram: 4249284608 Bytes
Used Ram: 37171200 Bytes
Done!
Release graphics data........ Done!
Release game data............
Unload 'Flash' ............done.
Unload 'Axel' ............done.
Unload 'Blaze' ............done.
Unload 'Haggar' ............done.
Unload 'Guy' ............done.
Unload 'Cody' ............done.
Unload 'Carlos' ............done.
Unload 'Lucia' ............done.
Unload 'Jessica' ............done.
Unload 'Adam' ............done.
Unload 'Sammy' ............done.
Unload 'Phone' ............done.
Unload 'Sandwich' ............done.
Unload 'Drum' ............done.
Unload 'Knife' ............done.
Unload 'Tires' ............done.
Unload 'Barrel' ............done.
Unload 'Radio' ............done.
Unload 'Zack' ............done.
Unload 'Bigben' ............done.
Release game data............ Done!
Release timer................ Done!
Release input hardware....... Done!
Release sound system......... Done!
Release FileCaching System... Done!
**************** Done *****************
Fatal: No cache entry for 'billys1' within 'data/levels/sor/stage1a.txt'
