You may need to enable Debug mode temporarily to do this, but I suspect it's just a conflict caused by the order they are executing.
With Debug mode enabled, go to Admin CP > Appearance > Template Modifications
In the list find "Unread Post Count" and below that find "navigation".
Click on "navigation" and change the value of "Execution Order" from 10 to 100.
I think that should allow both add-ons to work together.