Initially I was trying to install 2.0.5th.deb version on ubuntu 14.04 but it was conflicting with exiting packeges and conf files to owerwrite.then I did
# sudo dpkg -i --force-overwrite slack-desktop-2.0.5-i386.deb
Which gave slack icon in ubuntu-applications,but unable to run with producing above error.
I replaced slack deb version with older one
# sudo dpkg -i slack-desktop-1.2.6-amd64.deb. (It was available on my server)
Initially I was trying to install 2.0.5th.deb version on ubuntu 14.04 but it was conflicting with exiting packeges and conf files to owerwrite.then I did 2.0.5-i386. deb applications, but unable to run with producing above error. 1.2.6-amd64. deb. (It was available on my server)
# sudo dpkg -i --force-overwrite slack-desktop-
Which gave slack icon in ubuntu-
I replaced slack deb version with older one
# sudo dpkg -i slack-desktop-
It is working fine now ... :)