package otrs2 3.3.5-1 failed to install/upgrade: subprocess installed post-installation script returned error exit status 255 can not uninstall a broken installation of otrs2

After upgrading my Ubuntu to 14.04, I was unable to remember mysql password for otrs2, now it's broken, and I can't un-install it.

ProblemType: Package
DistroRelease: Ubuntu 14.04
Package: otrs2 3.3.5-1
ProcVersionSignature: Ubuntu 3.13.0-39.66-generic 3.13.11.8
Uname: Linux 3.13.0-39-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.5
Architecture: amd64
Date: Sun Nov 23 12:21:22 2014
DuplicateSignature: package:otrs2:3.3.5-1:subprocess installed post-installation script returned error exit status 255
ErrorMessage: subprocess installed post-installation script returned error exit status 255
InstallationDate: Installed on 2013-12-12 (346 days ago)
InstallationMedia: Ubuntu 12.04.3 LTS "Precise Pangolin" - Release amd64 (20130820.1)
PackageArchitecture: all
SourcePackage: otrs2
Title: package otrs2 3.3.5-1 failed to install/upgrade: subprocess installed post-installation script returned error exit status 255
UpgradeStatus: Upgraded to trusty on 2014-08-30 (84 days ago)