Since posting I have checked for any indication as to what was causing this in the console. It appears to be something related to OptiFine. My friend has tried re-adding OptiFine to the modpack but it still won't work.
" [b#431] 2014-03-15 17:54:45 [iNFO] [sTDOUT] TConstruct Environment: DO NOT REPORT THIS CRASH! Unsupported mods in environment: optifine
[b#431] 2014-03-15 17:54:45 [iNFO] [sTDOUT] #@!@# Game crashed! Crash report saved to: #@!@# C:Users*****AppDataRoaming.technicmodpacksmy-modpack-tidy-testcrash-reportscrash-2014-03-15_17.54.45-client.txt
[b#431] 2014-03-15 17:54:45 [iNFO] [sTDOUT] Closing Custom Recipes log..."
EDIT: I added OptiFine to the modpack.jar instead following a guide. The modpack now works but Forge isn't loading at all. :l