[rdiff-backup-users] "Truncated header string" error, how to diagnose?

[Chris G]

I have just upgraded to rdiff-backup 1.1.15 and now a backup to a
remote system which used to work is now failing with the following
sent from cron by E-Mail:-

    Fatal Error: Truncated header string (problem probably originated remotely)

    Couldn't start up the remote connection by executing

        ssh -C address@hidden rdiff-backup --server

    Remember that, under the default settings, rdiff-backup must be
    installed in the PATH on the remote system.  See the man page for more
    information on this.  This message may also be displayed if the remote
    version of rdiff-backup is quite different from the local version (1.1.15).


And, no, the remote version of rdiff-backup isn't different from the
local version - that's what was wrong yesterday and I've fixed it!

It was working fine when there was version 1.0.5 at both ends, I had
to upgrade 'this' end to 1.1.15 to get rdiff-backup to work to another
system that has 1.1.15 and *that* backup is now working OK.

If I execute:-
    ssh -C address@hidden rdiff-backup --server

it returns immediately but with no errors.  If I add a -v I see:-

    debug1: Authentications that can continue: publickey,password
    debug1: Next authentication method: publickey
    debug1: Offering public key: /home/chris/.ssh/id_rsa
    debug1: Server accepts key: pkalg ssh-rsa blen 277
    debug1: read PEM private key done: type RSA
    debug1: Authentication succeeded (publickey).
    debug1: channel 0: new [client-session]
    debug1: Entering interactive session.
    debug1: Sending environment.
    debug1: Sending env LC_COLLATE = C
    debug1: Sending env LANG = en_US.UTF-8
    debug1: Sending env LC_CTYPE = en_GB.utf8
    debug1: Sending command: rdiff-backup --server
    debug1: client_input_channel_req: channel 0 rtype exit-signal reply 0
    debug1: channel 0: free: client-session, nchannels 1
    debug1: Transferred: stdin 0, stdout 0, stderr 0 bytes in 0.1 seconds
    debug1: Bytes per second: stdin 0.0, stdout 0.0, stderr 0.0
    debug1: Exit status -1
    debug1: compress outgoing: raw data 1168, compressed 775, factor 0.66
    debug1: compress incoming: raw data 409, compressed 397, factor 0.97

If I ssh to the remote for an interactive session and enter
"rdiff-backup --server" it does what's expected and sits waiting, it
doesn't exit.  "rdiff-backup --version" returns "rdiff-backup 1.1.15".

So what's wrong? 

The only thing that *might* be significant is that the rdiff-backup
1.1.5 installation on the remote is installed in my account there
whereas the 1.0.5 was a root/system installion.

-- 
Chris Green