Avira AntiVir Scan Engine returned error 1151

Hi,

We have been getting on more than 1 server the error msg at more than customer we support :

Customer = CompanyX. Component = Servername Date : 18-04-2012 13:34
Event : Scanner ‘Avira AntiVir Scan Engine’ reported 1 consecutive errors!Current error description:Scanner ‘Avira AntiVir Scan Engine’ returned error 1151 (Unmapped return code 1151 mapped to ERROR.).

Does anyone have a clue to the cause of this error ?