package mercurial 3.1.2-2+deb8u1build0.15.04.2 failed to install/upgrade: subprocess installed post-installation script returned error exit status 128

THE APPLET CRASHES ON STARTUP AND SHUTDOWN. iN ADDITION, THE PROGRAM BOOTS INTO A "DOS LIKE" PROMPT ASKING FOR USER NAME AND PASSWORD. HOWEVER, IT DOESNOT ACCEPT EITHER. CONSEQUENTLY, I PRESS CTRL ALT DEL AND IT WILL THEN BOOT INTO THE SELECTION SCREEN ASKING FOR A RESPONSE REGARDING CONTINUEING WITH UNBUNTU, ADVANCED OPTION OR MEMORY TEST. THE ONLY SELECTION THAT WORKS IS TO CHOSE THE OPTION THAT IS NOT A RECOVERY BOOT. SORRY, I FORGOT THE NAME. i AM A FIRST TIME NOVICE. JUST GETTING BAPTIEZED INTO THIS VERY COOL OS WORLD. ANY HELP IS MUCH APPRECIATED.

THANKS

ProblemType: Package
DistroRelease: Ubuntu 15.04
Package: mercurial 3.1.2-2+deb8u1build0.15.04.2
ProcVersionSignature: Ubuntu 3.19.0-22.22-generic 3.19.8-ckt1
Uname: Linux 3.19.0-22-generic i686
ApportVersion: 2.17.2-0ubuntu1.1
Architecture: i386
Date: Tue Jun 30 10:54:45 2015
DuplicateSignature: package:mercurial:3.1.2-2+deb8u1build0.15.04.2:subprocess installed post-installation script returned error exit status 128
ErrorMessage: subprocess installed post-installation script returned error exit status 128
InstallationDate: Installed on 2015-04-27 (73 days ago)
InstallationMedia: Ubuntu 14.10 "Utopic Unicorn" - Release i386 (20141022.1)
RelatedPackageVersions:
 dpkg 1.17.25ubuntu1
 apt 1.0.9.7ubuntu4.1
SourcePackage: mercurial
Title: package mercurial 3.1.2-2+deb8u1build0.15.04.2 failed to install/upgrade: subprocess installed post-installation script returned error exit status 128
UpgradeStatus: Upgraded to vivid on 2015-05-25 (44 days ago)