apt-get update redmine: E: Sub-process /usr/bin/dpkg returned an error code (1)

SYMPTOM:
some apt-get update operation hangs or fails with error message E: Sub-process /usr/bin/dpkg returned an error code (1)

IMPACT:
Any subsequent package operation fails since there are broken packages

DIAGNOSE:
apt-get install --fix-broken
Reading package lists... Done
Building dependency tree
Reading state information... Done
0 upgraded, 0 newly installed, 0 to remove and 5 not upgraded.
1 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Setting up redmine (3.2.1-2) ...
Determining localhost credentials from /etc/mysql/debian.cnf: succeeded.
dbconfig-common: writing config to /etc/dbconfig-common/redmine/instances/default.conf
dbconfig-common: flushing administrative password
rake aborted!
Gem::LoadError: Specified 'mysql' for database adapter, but the gem is not loaded. Add `gem 'mysql'` to your Gemfile (and ensure its version is at the minimum required by ActiveRecord).
/usr/share/redmine/lib/plugins/acts_as_activity_provider/init.rb:2:in `block in <top (required)>'
/usr/share/redmine/config/initializers/00-core_plugins.rb:12:in `eval'
/usr/share/redmine/config/initializers/00-core_plugins.rb:12:in `block in <top (required)>'
/usr/share/redmine/config/initializers/00-core_plugins.rb:2:in `each'
/usr/share/redmine/config/initializers/00-core_plugins.rb:2:in `<top (required)>'
/usr/share/redmine/config/environment.rb:14:in `<top (required)>'
Gem::LoadError: mysql is not part of the bundle. Add it to Gemfile.
/usr/share/redmine/lib/plugins/acts_as_activity_provider/init.rb:2:in `block in <top (required)>'
/usr/share/redmine/config/initializers/00-core_plugins.rb:12:in `eval'
/usr/share/redmine/config/initializers/00-core_plugins.rb:12:in `block in <top (required)>'
/usr/share/redmine/config/initializers/00-core_plugins.rb:2:in `each'
/usr/share/redmine/config/initializers/00-core_plugins.rb:2:in `<top (required)>'
/usr/share/redmine/config/environment.rb:14:in `<top (required)>'
Tasks: TOP => db:migrate => environment
(See full trace by running task with --trace)
dpkg: error processing package redmine (--configure):
 subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
 redmine
E: Sub-process /usr/bin/dpkg returned an error code (1)

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: redmine 3.2.1-2 [modified: usr/share/redmine/config/environment.rb]
ProcVersionSignature: Ubuntu 4.4.0-24.43-generic 4.4.10
Uname: Linux 4.4.0-24-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
Date: Sun Jul 17 13:26:13 2016
PackageArchitecture: all
SourcePackage: redmine
UpgradeStatus: Upgraded to xenial on 2016-06-13 (34 days ago)