Also have this issue on SGS2, worked fine untill 2 days ago... now I constantly receive errors from the latter versions of the application.

(Authentication failure, certificate missing, signature failure)
I've gone back to version 1.7.2 (Current is 1.8.1) by downloading it through Aptoide, although it rolls back on a few features... a few working features is better than lots of unworkable features!
Note: This seems to be account specific... I can login to other accounts using version 1.8.1, just not my own. (I have tried many other methods of getting the latest version to work with my account, even as far as slamming my phone through Odin a few times)