Quote from taj1994
Not sure if you figured it out or not, but it's not an error. It just takes a minute or two extra to load when you have lots of mods
No, actually, it's a real error, I've let it sit there for at least 10 minutes and it stays with the window showing Not responding for as long as I let it sit there. The console window stops displaying any messages, so it just basically stops doing anything at all.
I have just let it go and given up on it, moved on to other things (trying FTB's Agrarian Skies currently), so I'm not worried about it.