Can't open mods/modpacks

[Arem567]

Here's a more detailed description of my problem:

I am able to open the launcher, and my account is authenticated with minecraft.net, however, even if the modpack is already downloaded, I am unable to actually open the modpack. After that, the launcher closes, and the modpack doesn't open.

Additional Information:

I am on OSX 10.7.5, running Java version 1.6.0_51.

Thanks.