I had the same problem while the clash was on and reloading the game client page worked. Now that clash 57 is finished it no longer works.
I've closed and reopened the game client page several times and the same error message keeps coming up. I currently can't play a game or even watch a replay.
I've cleared my cache, checked my internet connection, closed and re-opened the browser, tried different browsers and restarted my laptop but keep getting stuck at the same error message when loading.