(In reply to comment #2)
> I have sent the syncevolution-log.html of the sync that ends with error
> 10400 to your gmx account. The next sync will force a slow-sync and stop,
> because I have forbidden slow-syncs. Do you also need the log from this next
> sync?

No, the error is in the log that you sent. It looks like a SyncML protocol
violation by the Memotoo server:

[2013-06-09 18:38:07.564] 'processCmd' - Processing incoming command, Cmd=Sync,
IncomingMsgID=4, CmdID=2 [--][++] [->end] [->enclosing]

    [2013-06-09 18:38:07.565] Created command 'Status' (outgoing)
    [2013-06-09 18:38:07.565] Processing Sync, Source='note', Target='./memo'
    [2013-06-09 18:38:07.565] Sync command not allowed outside of sync phase
(-> 403)
    –
    [2013-06-09 18:38:07.565] 'SessionAbort' - Aborting Session, Status=400,
ProblemSource=LOCAL [--][++] [->end] [->enclosing]
        [2013-06-09 18:38:07.565] WARNING: Aborting Session with Reason Status
400 (LOCAL problem) ***

My guess is that you can work around this by limiting syncs to just one source
at a time:
syncevolution memotoo addressbook
syncevolution memotoo calendar
syncevolution memotoo todo
syncevolution memotoo memo

I'll contact the Memotoo admin and see whether he has an opinion about this.