Hey everyone, thanks for the further posts on this error with Hearthstone.
Since the initial reports in the start of this thread, we’ve been looking into the additional reports for that by ticket and currently our developers are looking into this further as mentioned here.
At the moment the normal workarounds for that error aren’t working and those may have been advised by ticket while this was still being reviewed in the earlier reports.
The error seems to be affecting some accounts attempting to connect to the EU region, though allowing play in other regions still. While that’s been looked into by our developers you may want to play in other regions temporarily.