... which leaves the question why the migration manager GUI allows the port to be changed in the first place but anyway I changed the port to 22 and it started.
Nevertheless the next error has risen up:
[10:31:13|DEBG:32218
.Ssh] remote stderr -> 08:31:11 INFO FileFinder: pwd resolved to /bin/pwd
08:31:11 INFO ------------------------------------------------------------
08:31:11 INFO FILE storage initialized.
08:31:11 INFO Base directory: /var/cache/20110707102814554
08:31:11 INFO Gzip bundles: no
08:31:11 INFO Bundle split size: do not split
08:31:11 INFO ------------------------------------------------------------
08:31:11 INFO ------------------------------------------------------------
08:31:11 INFO Migration status reporting initialized.
08:31:11 INFO Status file: /var/cache/20110707102814554/dumping-status.xml
08:31:11 INFO ------------------------------------------------------------
08:31:11 INFO New connection: mysql DBI connection. db confixx, user confixx, host localhost
08:31:11 WARN be6b31eb-7acf-44d6-8436-a9d80039c857 Expected to have exactly one row in result set
Use of uninitialized value $clientSystemDomain in concatenation (.) or string at Agent.pm line 249, <STDIN> line 6.
Use of uninitialized value $domainName in concatenation (.) or string at Agent.pm line 298, <STDIN> line 6.
Use of uninitialized value $domainName in concatenation (.) or string at Agent.pm line 531, <STDIN> line 6.
08:31:12 INFO FileFinder: tar resolved to /bin/tar
08:31:12 INFO Executing bundle producer: '/bin/tar -f - -c -h .' in /tmp/migration_dump_mail
Use of uninitialized value $emailAddress in pattern match (m//) at Agent.pm line 588.
Use of uninitialized value $domainName in concatenation (.) or string at Agent.pm line 697.
08:31:12 INFO FileFinder: idnconv resolved to /usr/bin/idnconv
Use of uninitialized value $domainName in concatenation (.) or string at Agent.pm line 531.
08:31:12 INFO FileFinder: tar resolved to /bin/tar
08:31:12 INFO Executing bundle producer: '/bin/tar -f - -c -h .' in /tmp/migration_dump_mail
Use of uninitialized value $emailAddress in pattern match (m//) at Agent.pm line 588.
Use of uninitialized value $domainName in concatenation (.) or string at Agent.pm line 697.
Use of uninitialized value $domainName in concatenation (.) or string at Agent.pm line 531.
08:31:13 INFO FileFinder: tar resolved to /bin/tar
08:31:13 INFO Executing bundle producer: '/bin/tar -f - -c -h .' in /tmp/migration_dump_mail
Use of uninitialized value $emailAddress in pattern match (m//) at Agent.pm line 588.
Use of uninitialized value $domainName in concatenation (.) or string at Agent.pm line 697.
Use of uninitialized value $domainName in concatenation (.) or string at ContentDumper.pm line 15.
08:31:13 INFO FileFinder: tar resolved to /bin/tar
08:31:13 INFO Executing bundle producer: '/bin/tar -f - -c --anchored -X '/tmp/filemDtETQ' .' in /home/htdocs/web0/html//
Use of uninitialized value $domainName in concatenation (.) or string at Agent.pm line 1146.
'undef' value passed to XmlNode::setAttribute for 'name' at shared_legacy/XmlNode.pm line 103.
at shared_legacy/XmlNode.pm line 103
XmlNode::setAttribute('XmlNode=HASH(0x89944ec)', 'name', undef) called at shared_legacy/XmlNode.pm line 73
XmlNode::_init('XmlNode=HASH(0x89944ec)', 'domain', 'attributes', 'HASH(0x86725c4)', 'children', 'ARRAY(0x8968b74)') called at shared_legacy/XmlNode.pm line 24
XmlNode::new('XmlNode', 'domain', 'attributes', 'HASH(0x86725c4)', 'children', 'ARRAY(0x8968b74)') called at Agent.pm line 251
Agent::_getSystemDomainNode('web0', 'HASH(0x8672694)') called at Agent.pm line 152
Agent::getClient('web0') called at shared_legacy/DumpComposer.pm line 408
DumpComposer::_selectionDumpProcessClient('web0', 'ARRAY(0x88952dc)', 'HASH(0x8776114)', 'HASH(0x87a12ec)') called at shared_legacy/DumpComposer.pm line 276
DumpComposer::_walkTree(undef, 'HASH(0x88db3bc)', 'HASH(0x8776114)', 'HASH(0x87a12ec)') called at shared_legacy/DumpComposer.pm line 274
DumpComposer::_walkTree('HASH(0x87b6694)', 'HASH(0x88db3bc)', 'HASH(0x8776114)', 'HASH(0x87a12ec)') called at shared_legacy/DumpComposer.pm line 274
DumpComposer::_walkTree('HASH(0x889534c)', 'HASH(0x88db3bc)', 'HASH(0x8776114)', 'HASH(0x87a12ec)') called at shared_legacy/DumpComposer.pm line 57
DumpComposer::makeDump('/var/cache/20110707102814554', 'ARRAY(0x87a0efc)', 'ARRAY(0x82b8c64)', 'ARRAY(0x87a0eac)', undef, undef, undef, 1) called at shared_legacy/AgentCLI.pm line 198
AgentCLI::main() called at /var/cache/20110707102814554/Confixx.pl line 17
[10:31:13|DEBG:32218
.Ssh] Execution finished with return code 9