Unfortunately the log is not a console log so I'm going to list both possibilities that I know of for this error.
First it could be GregTech not liking where you have the pack installed. If anywhere in the folder structure leading to the pack are the words 'tekkit' or 'technic' GregTech will cause this crash with RedPower 2. You need to either install the mod packs somewhere else, like your desktop in an folder named FTB. Or remove GregTech.
The other possibility is that it is an ID Conflict between RedPower2 and a mod you've added to the pack. If you have added any mods to the pack then check out this
guide for fixing the conflicts. Change the new mod's config not RedPower2's. Be sure to check the console as it will probably give you the ID that is conflicting. Look here for more info about the logs if you need help getting the console to show up.
