Error while taking back up.

Before few month box of SQL has been crashed. We have almost database back with some tools and running application smoothly on it. But when i try to take backup of database at that time it gives error as below,

'The log scan number (3533468:412:0) passed to log scan in database '****' is not valid. This error may indicate data corruption or that the log file (.ldf) does not match the data file (.mdf). If this error occurred during replication, re-create the publication. Otherwise, restore from backup if the problem results in a failure during startup. (Microsoft SQL Server, Error: 9003)'

Would anyone help me to out of this?

I have even try to copy database but i am failed.

Thanks in Advance.