Exchange Backup fails :

I am running microsoft information store backup on B2D folder,backup running for 7 hours gives error : 

V-79-57344-759 - Unable to complete the operation for the selected resource using the specified options. The following error was returned when opening the Exchange Database file: '-528 The current log file is missing.

Could anyone suggest any reason for the above and possible solution.

All replies will be appreciated.

Thanks