+1 for this error this morning. It was coming in fine yesterday, but now it seems very very slow - it's been loading for a good 10 minutes, and only partway int the 'A' of my modpacks. I'm currently trying to figure out if there is any way to start the modpack(s) from the file explorer.
If it's loading these modpacks for at least 10 minutes each at startup (or whatever it is doing), I guess I should hide the ones I'm not using right now, but I don't understand what it's doing that's taking so much time.
Edit: It's now been loading revelation (which I have removed from the instances folder...) for over an hour. It did not try to load ATM4 (also removed).
By running minecraft.exe from the curse install location, I was able to run my modpack (though mine was glitchy so required making a new profile linked to where that pack was installed, and re-downloading forge and manually setting that up). Something to try!