This new launcher has messed up Curse Launcher

I'm having issues with the curse mod launcher as well. Basically the new launcher for Minecraft works fine when playing the vanilla game.
When trying to launch mods from curse it uses the new fancy launcher and prompts you to log in with your mojang account. Then when selecting a mod or normal game the launcher crashes or hangs on downloading updates.
Is there a workaround for this problem?

I am experiencing this as well, not remembering login, crashing on start of download. I have been digging into it further.

I have a temporary workaround:

1. Run the pack from curse so it can prepare the files. Then close the new minecraft launcher that comes up.
2. Run the new minecraft launcher like this, note you will have to adjust both paths to be the correct one for you with your username: "C:\Users\Corosus\Documents\Curse\Minecraft\Install\minecraft.exe" --workDir "C:\Users\Corosus\Documents\Curse\Minecraft\Install"

The use of --workDir is the fix that worked for me, curse launcher doesnt run with that argument.

Curse has suggested to me that it is a bug with the new launcher when run from a different directory.

Using windows 7, launcher version 2.0.713

I have also experienced the things Kevin mentioned, sans the crashes. However, i'd rather not have a temporary fix, and id like to know when this will be fixed.

Kevin Gagnon could you please explain this a little better? I don't know what to do with the text.

May be fixed:
https://twitter.com/MansOlson/status/826477447155765249

For those who have the new Minecraft launcher: It's updated to fix some issues with mods. If you were stuck on "Preparing...", try it now!

Using curse live(beta) version, and minecraft launcher 2.0.729 which I assume is the update MansOlson is referring to still freezes up at "Preparing..."

Curse has released a fix on their alpha release channel which works perfectly, no need to use my above workaround anymore.

Steps:
1. In curse, go to settings
2. In settings, click Minecraft
3. Scroll down to "Preferred release" and set it to alpha
4. Save changes and close settings
5. Click the question mark above the settings button
6. Click "about curse"
7. Click switch to alpha
8. Let curse install and restart

After all that you should be able to run your modpacks fine, works perfectly with new launcher. Hopefully they will push this fix to the live release sometime soon.

From MCL-5377 :

@unknown
This is a known issue with the new launcher and Curse. We're looking into it.

I tried your fix Kevin Gagnon and the launcher is now working properly, but I keep getting Java errors and crashes halfway through the pack loading. Does it for every pack on the Curse launcher. I'm on Windows 7.

Yes - as recent, i am also getting Errors, however i receive them as soon as i even attempt to load the pack.

This is actually an issue on Curse's end. They have a fix which will be rolled out soon, but you can get it from their Alpha build early if you want. I did, however, push out a "fix" that forces the old jar launcher if we detect curse, until they have their fix rolled out.