relay log file corrupted

Hello, I have a MySQL 4.1.14 replicating a 4.1.8 version. The slave stopped.
When I execute show slave status I see that the SQL thread is not running.
It raises no error code but the message:
'Could not parse relay log event entry. The possible reasons are: the
master's binary log is corrupted (you can check this by running
'mysqlbinlog' on the binary log), the slave's relay log is corrupted (you
can check this by running 'mysqlbinlog' on the relay log), a network
problem, or a bug in the master's or slave's MySQL code. If you want to
check the master's binary log or slave's relay log, you will be able to know
their names by issuing 'SHOW SLAVE STATUS' on this slave.'
Effectively, the realay log file is corrupted. It is truncated.
Even though, when I try to change the relay log file and the relay log pos
to start processing the next file (I don't mind to lose a few queries) I got
an error: [ServerLibros] ERROR 1105: Failed initializing relay log position:
Could not find target log during relay log initialization. (The file name is
ok. I also tried writing the whole path.)
If I change it using the file relay-log.info I got no error but the SQL
thread doesn't start to work.
I don't know what to do except stopping the servers making a buckup and
starting again with replication.

Matías