I'm getting error in viber icon which is as shown.
Can anyone give me solution to this problem?
Try also changing the /usr/share/applications/viber.desktop file to be like the one here:
[Desktop Entry] Name=Viber Comment=Viber VoIP and messenger Exec=env XDG_CURRENT_DESKTOP=Unity /opt/viber/Viber Icon=/usr/share/pixmaps/viber.png Terminal=false Type=Application Encoding=UTF-8 Categories=Network;Application; Path=
Got it from this (which applies to the elementaryPlus icon set, but it should work with the stock elementary icon theme as well).
This is what I did to make the Viber icons show up.
Try to add to your environment following parameters: XDG_CURRENT_DESKTOP=Unity QT_STYLE_OVERRIDE=""
you can put it into your .profile file