It could be restarted at any moment before the time window closes.
The countdown was stopped when two red lights were seen lighting up on a control board. It was not immediately clear whether this constituted a serious problem or whether officials were simply being cautious.
The launch window for the Ariane 5 ECA rocket is open from 20:49 CET until 22:10 CET.
More info at CNN
Update: News has reached us that Ariane 5 ECA took off successfully - 26 minutes after launch the XTAR-EUR was separated from the rocked and five minutes later the SLOSHSAT satellite also detached successfully