Hello, did you first uninstall the mini client before installing a new one?

Your flash player is up to date? also i know you stated you already cleared cache but can you try that once more and after you've done that, please refresh the game.
You could also clear your DNS-cache and the cache of the launcher browser.
To clear the DNS-cache, open a command prompt (“Windows” key +”R” key and inside the new window enter "cmd") and type inside the command "ipconfig /flushDNS".
The cache of the launcher browser can be cleared by using the *on "Game Doctor"

Was it working ok before? Did you do any software upgrades before this happen?

What Operative System are you using?