Looping to Playonline viewer right after clicking on 'Play on Test Server'

I have used the test server since it came out, nothing's changed in my test server files except it needed an update which I did this afternoon...

Now everytime I try to login it starts looping to Playonline viewer right after clicking on 'Play on Test Server'

Anyone had this problem?

Thanks for your help!

EDIT: I should add that it works fine if I play using normal method within the test client, the left button.

I had the same Issue.
Com Rep on an another language forum suggested to deinstall/install.

I did that with the old downloaded files (still had them) didn't run.

Downloaded again. Installed again. Works.

Appears to be a bug with the old Files in some cases.