The following is taken from ubuntu documentation:- click here
'Broken packages' are packages that have unsatisfied dependencies. If broken packages are detected, Synaptic will not allow any further changes to the system until all broken packages have been fixed.
To fix broken packages
Choose Edit > Fix Broken Packages from the menu.
Choose Apply Marked Changes from the Edit menu or press Ctrl + P.
Confirm the summary of changes and click Apply.