Yesterday I decided to add a mod to an FTB modpack (Etho's) and after hours of trying out versions (they didn't specify the forge version it needed) I found out it worked only with the latest forge version. I found on Reddit how to upgrade a modpack's Forge, so I did... And I'm not sure if I screwed up that "upgrade" or if it's something else.

 

Everything seems to be working up until the "stitching textures" part. At first the memory usage started going up non-stop until it crashed, restarting seemed to fix that. Then I tried allocating less (weird, but it worked a couple times) memory and more, only changing how long it took to take me back to the launcher again.

 

Here's the log, if you need the full thing just tell me: http://pastebin.com/raw/UgHb6pb9

Update to 1.8+