Hello John,
Added the sleep 10, but still got the problem. I checked the proftpd configuration but it looks good to me.
In the logs on the remote host (with DA) I only see this messages:
::ffff:12.345.67.89 UNKNOWN dionwa [10/Mar/2011:01:12:24 +0100] "CLNT NcFTPPut 3.2.2 linux-x86_64-glibc2.5" 500 -
::ffff:12.345.67.89 UNKNOWN dionwa [10/Mar/2011:01:12:28 +0100] "STOR user.admin.**********.tar.gz" 451 37060928
Mar 10 01:12:24 srv1 proftpd[26411]: 34.56.789.01

:ffff:12.345.67.89[::ffff:12.345.67.89]) - Preparing to chroot to directory '/home/dionwa'
Mar 10 01:12:28 srv1 proftpd[26411]: 34.56.789.01

:ffff:12.345.67.89[::ffff:12.345.67.89]) - notice: user dionwa: aborting transfer: Input/output error
I have no clue what's wrong.
in this message i've changed real ip's for fake ones.