Below the complete error log.
Installation started in background
Getting bootstrapper packages to installation list:
skip package 'pp12.0.18-bootstrapper-12.0.18-cos6.build1200140617.18.x86_64' from component common - there is same or newer version of this package is installed (in system pp12.0.18-bootstrapper-12.0.18-cos6.build1200140617.18.x86_64)
Following bootstrapper packages will be installed: (empty)
----------------
Getting packages to installation list:
skip package 'plesk-base-12.0.18-cos6.build1200140606.15.x86_64' from component common - there is same or newer version of this package is installed (in system plesk-base-12.0.18-cos6.build1200140606.15.x86_64)
skip package 'psa-12.0.18-cos6.build1200140606.15.x86_64' from component common - there is same or newer version of this package is installed (in system psa-12.0.18-cos6.build1200140606.15.x86_64)
skip keypackage 'psa-12.0.18-cos6.build1200140606.15.x86_64' from component common - same or newer version of this package is already installed (in system psa-12.0.18-cos6.build1200140606.15.x86_64)
Following packages will be installed: (empty)
----------------
Loaded plugins: fastestmirror, presto, priorities
Loading mirror speeds from cached hostfile
* atomic: mir01.syntis.net
* base: centos.mirror.triple-it.nl
* epel: ftp.nluug.nl
* extras: centos.mirror.triple-it.nl
* updates: centos.mirror.triple-it.nl
430 packages excluded due to repository priority protections
Patch for plesk 12.0.18 will be installed.
Bezig met installatie van patches?
FileFetcher: get file (~empty)/PSA_12.0.18/microupdates/MU4/common/_usr_local_psa_PMM_agents_shared_Storage_Storage.pm
Downloaden van het bestanden PSA_12.0.18/microupdates/MU4/common/_usr_local_psa_PMM_agents_shared_Storage_Storage.pm: voltooid.
FileFetcher: get file (~empty)/PSA_12.0.18/microupdates/MU4/rpm-CentOS-6-x86_64/_usr_local_psa_admin_sbin_pmm-ras
Downloaden van het bestanden PSA_12.0.18/microupdates/MU4/rpm-CentOS-6-x86_64/_usr_local_psa_admin_sbin_pmm-ras: voltooid.
FileFetcher: get file (~empty)/PSA_12.0.18/microupdates/MU4/rpm-CentOS-6-x86_64/_usr_local_psa_admin_sbin_deployer
Downloaden van het bestanden PSA_12.0.18/microupdates/MU4/rpm-CentOS-6-x86_64/_usr_local_psa_admin_sbin_deployer: voltooid.
FileFetcher: get file (~empty)/PSA_12.0.18/microupdates/MU5/common/_usr_local_psa_admin_bin_plesk_agent_manager
Downloaden van het bestanden PSA_12.0.18/microupdates/MU5/common/_usr_local_psa_admin_bin_plesk_agent_manager: Error: error during prepare patch plesk-12.0.18~patch5
Kan het pakket http://autoinstall.plesk.com/PSA_12.../_usr_local_psa_admin_bin_plesk_agent_manager niet downloaden:
The requested URL returned error: 404
Niet alle pakketten zijn geïnstalleerd.
Probeer de installatie van pakketten later opnieuw.
Neem contact op met de technische ondersteuning van het product.
The package http://autoinstall.plesk.com/PSA_12.../_usr_local_psa_admin_bin_plesk_agent_manager could not be downloaded because it could not be found (The requested URL returned error: 404).
Installation started in background
Getting bootstrapper packages to installation list:
skip package 'pp12.0.18-bootstrapper-12.0.18-cos6.build1200140617.18.x86_64' from component common - there is same or newer version of this package is installed (in system pp12.0.18-bootstrapper-12.0.18-cos6.build1200140617.18.x86_64)
Following bootstrapper packages will be installed: (empty)
----------------
Getting packages to installation list:
skip package 'plesk-base-12.0.18-cos6.build1200140606.15.x86_64' from component common - there is same or newer version of this package is installed (in system plesk-base-12.0.18-cos6.build1200140606.15.x86_64)
skip package 'psa-12.0.18-cos6.build1200140606.15.x86_64' from component common - there is same or newer version of this package is installed (in system psa-12.0.18-cos6.build1200140606.15.x86_64)
skip keypackage 'psa-12.0.18-cos6.build1200140606.15.x86_64' from component common - same or newer version of this package is already installed (in system psa-12.0.18-cos6.build1200140606.15.x86_64)
Following packages will be installed: (empty)
----------------
Loaded plugins: fastestmirror, presto, priorities
Loading mirror speeds from cached hostfile
* atomic: mir01.syntis.net
* base: centos.mirror.triple-it.nl
* epel: ftp.nluug.nl
* extras: centos.mirror.triple-it.nl
* updates: centos.mirror.triple-it.nl
430 packages excluded due to repository priority protections
Patch for plesk 12.0.18 will be installed.
Bezig met installatie van patches?
FileFetcher: get file (~empty)/PSA_12.0.18/microupdates/MU4/common/_usr_local_psa_PMM_agents_shared_Storage_Storage.pm
Downloaden van het bestanden PSA_12.0.18/microupdates/MU4/common/_usr_local_psa_PMM_agents_shared_Storage_Storage.pm: voltooid.
FileFetcher: get file (~empty)/PSA_12.0.18/microupdates/MU4/rpm-CentOS-6-x86_64/_usr_local_psa_admin_sbin_pmm-ras
Downloaden van het bestanden PSA_12.0.18/microupdates/MU4/rpm-CentOS-6-x86_64/_usr_local_psa_admin_sbin_pmm-ras: voltooid.
FileFetcher: get file (~empty)/PSA_12.0.18/microupdates/MU4/rpm-CentOS-6-x86_64/_usr_local_psa_admin_sbin_deployer
Downloaden van het bestanden PSA_12.0.18/microupdates/MU4/rpm-CentOS-6-x86_64/_usr_local_psa_admin_sbin_deployer: voltooid.
FileFetcher: get file (~empty)/PSA_12.0.18/microupdates/MU5/common/_usr_local_psa_admin_bin_plesk_agent_manager
Downloaden van het bestanden PSA_12.0.18/microupdates/MU5/common/_usr_local_psa_admin_bin_plesk_agent_manager: Error: error during prepare patch plesk-12.0.18~patch5
Kan het pakket http://autoinstall.plesk.com/PSA_12.../_usr_local_psa_admin_bin_plesk_agent_manager niet downloaden:
The requested URL returned error: 404
Niet alle pakketten zijn geïnstalleerd.
Probeer de installatie van pakketten later opnieuw.
Neem contact op met de technische ondersteuning van het product.
The package http://autoinstall.plesk.com/PSA_12.../_usr_local_psa_admin_bin_plesk_agent_manager could not be downloaded because it could not be found (The requested URL returned error: 404).