There are two differences showing up in the logs in start up. First, the PC with the problems uses forward slashes in the file addresses, and it seems to be missing a second and third set of object loads after the begin openrct2 loop. I've bolded the lines before and after the difference.
PC1:
VERBOSE: Source_Sample::LoadCSS1(C:\Program Files (x86)\Atari\RollerCoaster Tycoon 2 Triple Thrill Pack\Data\css1.dat, 59)
VERBOSE: Source_Sample::LoadCSS1(C:\Program Files (x86)\Atari\RollerCoaster Tycoon 2 Triple Thrill Pack\Data\css1.dat, 60)
VERBOSE: Source_Sample::LoadCSS1(C:\Program Files (x86)\Atari\RollerCoaster Tycoon 2 Triple Thrill Pack\Data\css1.dat, 61)
VERBOSE: Source_Sample::LoadCSS1(C:\Program Files (x86)\Atari\RollerCoaster Tycoon 2 Triple Thrill Pack\Data\css1.dat, 62)
VERBOSE: begin openrct2 loop
VERBOSE: HardwareDisplay: false VERBOSE: Source_Sample::LoadWAV(C:\Program Files (x86)\Atari\RollerCoaster Tycoon 2 Triple Thrill Pack\Data\css2.dat)
VERBOSE: loading scenario details, C:\Program Files (x86)\Atari\RollerCoaster Tycoon 2 Triple Thrill Pack\Scenarios\Afri
ca - African Diamond Mine.SC6
PC2:
VERBOSE: Source_Sample::LoadCSS1(C:/Program Files (x86)/Atari/RollerCoaster Tycoon 2 Triple Thrill Pack\Data\css1.dat, 59)
VERBOSE: Source_Sample::LoadCSS1(C:/Program Files (x86)/Atari/RollerCoaster Tycoon 2 Triple Thrill Pack\Data\css1.dat, 60)
VERBOSE: Source_Sample::LoadCSS1(C:/Program Files (x86)/Atari/RollerCoaster Tycoon 2 Triple Thrill Pack\Data\css1.dat, 61)
VERBOSE: Source_Sample::LoadCSS1(C:/Program Files (x86)/Atari/RollerCoaster Tycoon 2 Triple Thrill Pack\Data\css1.dat, 62)
VERBOSE: begin openrct2 loop
VERBOSE: HardwareDisplay: false VERBOSE: Source_Sample::LoadWAV(C:/Program Files (x86)/Atari/RollerCoaster Tycoon 2 Triple Thrill Pack\Data\css2.dat)
VERBOSE: loading required objects
VERBOSE: loading object, C:/Program Files (x86)/Atari/RollerCoaster Tycoon 2 Triple Thrill Pack\ObjData\MFT.DAT
VERBOSE: loading object, C:/Program Files (x86)/Atari/RollerCoaster Tycoon 2 Triple Thrill Pack\ObjData\BALLN.DAT
VERBOSE: loading object, C:/Program Files (x86)/Atari/RollerCoaster Tycoon 2 Triple Thrill Pack\ObjData\BURGB.DAT
VERBOSE: loading object, C ( ...continues for about 800 lines, then...)
VERBOSE: finished loading required objects VERBOSE: loading scenario details, C:/Program Files (x86)/Atari/RollerCoaster Tycoon 2 Triple Thrill Pack\Scenarios\Afri
ca - African Diamond Mine.SC6
NOTE: Changing the game_path on PC1 from using forward slash to double back slash (as it is on PC2) didn't fix the issue.