Arianespace decided to stop preparing for flight again. There was no next launch date announced but Company is targeting for 25th April 2016.
UPDATE: 25 April 2016 - Launch was set for 25th April 2016, 21:02 GMT, IMU was changed and testing went correctly.
UPDATE: 25 April 2016 - Russian specialists discovered that reason of the problem was faulty IMU. Unit will be swapped with new one and it is highly probable that launch will be set for 25th April 2016.
Third launch attempt of 14th Soyuz-2.1A launch from Guiana Space Center was cancelled at 20:18 GMT in the moment when Soyuz was already tanked. Even at 21:46 GMT everything was set to "launch” and mobile gantry's doors were opened - fueling was finished at 21:36 GMT. Unfortunately flight engineers decided to halt procedure, but this time reason was different than yesterday and two days ago and it was not caused by poor weather conditions. It was more serious; according to post on Twitter published by CEO of Arianespace, Stephane Israel:
"An anomaly has occurred on the SYZ Inertial Measurement Unit. Stop for tonight. Work in progress to confirm launch tomorrow."
It is sure that some problems were spotted in launch vehicle and in its crucial system. Inertial Measurement Unit (IMU) is instrument which is measuring in real time force, angular rate and magnetic field and transfer data to onboard computer. It is using various sensors like accelerometer, gyroscope or magnetometer. Without accurate data from IMU rocket launch would probably finish with failure. Anomaly could be linked with wrong data interpretation by onboard computer or what is more probable, that one of the sensors was giving wrong values. Now technicians will check every sensor and analyze log from computers to figure out where was the problem. Of course it will take time, but still most possible is postponing launch for next 24 hours.