strange migration problem/error

[Softterrier]

Hallo Sirs,

unfortunately I got an interrupt during a migration process.
The error message is the following (s. also attachments
<?xml version="1.0" encoding="UTF-8"?>
<restore status="error" log-location="">
<deploy status="error" log-location="">
<message code="" severity="error" id="">
<description>PMMCli was finished with exit code 1</description>
</message>
</deploy>
</restore>

Migration happened from a Debian server to an Ubuntu server (both have actual op.sys. and the same Plesk version)
Both are configured in Customized-Mode (i.e. no reseller mode!).
I attached error log files.
The attached log files show some processes. But I cannot conclude anything from it.
The log pmmcli.log does not show any problem allthough I had this final error message in my browser...

Please tell me...
1.) ...what the error message means
2.) ...how I can avoid this error in the future
3.) ...how I can repeat a migration (any special conditions?)
4.) ...all the conditions (between two servers) that have to be fulfilled so that there should not occure a migration problem.

Many thanks for your detailed answers!

Best regards,
Falk Hertel