This is very odd. I'm getting the same thing this evening. I tried it on my laptop at work this morning and it worked perfectly, downloaded and ran the Direwolf20 pack. I copied my installation directory over onto my home laptop but the launcher fails to connect to creeperrepo.net again.
Is there any way that I can run the game offline without having to connect to creeperrepo.net? Is there a chance that my copied installation won't work on this laptop because, for example, of a different Java version? Both are WIndows 7. I have no idea what Java my work machine was runing, but this one has both Java 7 Update 9 v7.0.90 and Java(TM) 6 Update 31 v6.0.310 listed in Programs and Features. Should I remove one of them?