I'm having the problem as well. I have tried the .jar download (0.5.4.4) [on mac]. I have also tried the .exe download (0.5.4.4) [on windows]. There is no error report, if i try logging in on technic, tekkit or vanilla, the updater, goes through two bars and on the third bar it stops 90-99% before finishing. A window pops up with "Upate Failed". I've tried downloading and redownloading again and again. No success.