Fritzing unrouted connections with Autoroute
I have not used Frtizing, but generally when autorouters leave unrouted connections it means they can't find a way to route them without breaking design rules. 

Although they have come a long way, many folk still do some/most/all their routing manually, maybe using the autorouter first to get an idea of how easy it will be to route the board and optimise placement. They work better for some designs than others, usually layout/rule setup is a very important factor in how well they will perform.   

A few suggestions:


Alter design rule tolerances and try again (e.g. smaller trace clearance/width)
Set router to try harder (usually a setting to specify how many times it will try before picking best option/giving up) or change routing topology.
Add another layer to make routing easier (or add ground/power plane)
Alter placement of components/board size to make more space, especially in congested areas.
Give as much prior direction to autorouter (set up net areas, layers etc, if possible)
Try another autorouter :-)
Finish routing by hand