If you cancel the technic SSP update screen, it won't ever stop checking.

[Doodler]

I clicked login, and then the screen asked me if I wanted to update. I clicked cancel and the bar gets stuck on "Checking for Technic SSP update" and none of the buttons are clickable. It works perfectly fine when I click yes.

The "Always use development builds" option is checked.

[KakerMix]

You can get around this by selecting vanilla from the drop-down menu, it will free up your controls again. We are aware of this bug.