Just a little reading on the subject: Oracle does not support Java 6 anymore. It is no longer the recommended Java version for Mac users. Java 7 requires OSX 10.7.3 or higher (Lion). There's a few various ways to get Java 7 on Snow Lion. From here, I found this way to install it. It appears to be something that may void a warranty if done though. Only solution I have found that is kosher: update OS. Updating to Mavericks seems to be free. Mavericks users must use Java 7 for FTB to work on 1.6.4. It's been this way since before we even had 1.6.4 mod packs. To play older packs, they will need to update to LWJGL 2.9 or higher in those packs.