From ESA:

SOHO went into Emergency Sun Reacquisition (ESR) mode last night (ESR-27). The cause was the same as for ESA-26 in August 2010: false trigger of the Course Sun Pointing Attitude Anomaly Detector (CSPAAD). SOHO is now back in Course Roll Pointing mode (CRP) and will stay there over the weekend. Early next week we will roll the spacecraft back to normal roll attitude.