After update, Synaptic Manager in Ubuntu sometimes gives error
Unable to get exclusive lock. This usually means that another package management application(like apt-get or aptitude) is already running. Please close that application first.
As the message says, it means that it is already running. By default, Ubuntu runs a check after reboot — not immediately, but some time within.
Generally, it is not advised to pause an update. Once an update has started, allow it to run its course. So, wait for some time, at least 30 minutes or more to complete the background update.
In case the update takes a while, open a terminal (Ctrl+Alt+T) and type this
ps aux | grep dpkg | grep -v grep
If it shows any text then it means system is still updating, just wait for next update.