application updates, autehntication error, transient network issue

I incurred the issue after adding the following statement to the Sources List:

deb http://ftp.de.debian.org/debian sid main

The running the native Software Updater application on Ubuntu 15.10. I need this software to install libpolarssl-dev_1.3.9-2.1_i386.deb in an attempt to install and use dislocker to unencrypt/access a bitlocked HDD.

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: ubuntu-release-upgrader-core 1:15.10.13
ProcVersionSignature: Ubuntu 4.2.0-16.19-generic 4.2.3
Uname: Linux 4.2.0-16-generic i686
ApportVersion: 2.19.1-0ubuntu3
Architecture: i386
CasperVersion: 1.365
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Wed Nov 4 07:03:19 2015
LiveMediaBuild: Ubuntu 15.10 "Wily Werewolf" - Release i386 (20151021)
PackageArchitecture: all
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: No upgrade log present (probably fresh install)
VarLogDistupgradeTermlog: