Symptoms

Plesk upgrade failed with error:

psa-proftpd-xinetd-1.3.5-6.el5.art.x86_64 from installed has depsolving problems
  --> Missing Dependency: psa-proftpd = 1.3.5-6.el5.art is needed by package psa-proftpd-xinetd-1.3.5-6.el5.art.x86_64 (installed)
Exception: Failed to solve dependencies:
Missing Dependency: psa-proftpd = 1.3.5-6.el5.art is needed by package psa-proftpd-xinetd-1.3.5-6.el5.art.x86_64 (installed)

The following commands show that psa-proftpd package is installed through non-Plesk repository:

# rpm -qi psa-proftpd-1.3.4c-4.el5.art
# rpm -qi psa-proftpd-xinetd-1.3.4c-4.el5.art

Cause

Packages installed from third-party repository conflicts with Plesk packages.

Resolution

1. Remove psa-proftpd packages from Atomic repository:

   # rpm -e psa-proftpd-xinetd-1.3.5-6.el5.art --nodeps
   # rpm -e psa-proftpd-1.3.5-6.el5.art --nodeps
   

2. Make sure Atomic repository is disabled.

3. Install proftpd service using Plesk installer:

   # plesk installer