I've already did bit it didn't work.

What I did now was to disable the change tracking, do backup, and enable the change tracking again.

It seems is working well now.

Thanks.

Sorry for my late reply.

Finally my hard disk failed and I had to recover the database from the backups.

Thanks to all for your help.

I ran a

DBCC CHECKTABLE ("table") WITH PHYSICAL_ONLY;

cause the DB is really big and I got these errors:

Msg 8944, Level 16, State 16, Line 2

Table error: Object ID 0, index...

The table has already a clustered index.

from the logs, I can see there was a dump :

* ...