I've been encountering the same error. After trying many things I discovered I can reliably avoid this problem by delting the following file:
.technic/lastlogin
On windows, this is located in %APPDATA%/.technic/lastlogin
I also kill any instances of "javaw.exe" running in Task Manager. Then I can restart the launcher and it works. The only consequence is I have to re-enter my login credentials.
If I choose to "remember my password" then I have to do this EVERY time I want to start the launcher. If I don't select "remember" then it works every time.
