Patch 1.0.2 was released today and the Americas servers are currently down for maintenance/patching. Europe and Asia players who have downloaded the wrong client, English (US), will have had their clients patched before the EU servers, thus causing an inability to log-in to their EU characters despite the EU servers being up and running. You know you have this error if the pre-launcher states that "Game is ready" but when signing-in you are asked to update the game (the game crashes soon after).
The best way to fix this is to uninstall Diablo 3 and log into your account on Battle.net and change your 'Full Game Client' to English (EU) or another language associated with the region you are playing in and re-installing.
I have just done so myself and can confirm that I am logged into EU on client 1.0.1 having previously had issues logging in with 1.0.2 onto EU characters.
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