I am trying to install ARC breakers at my home. I have a couple of bedrooms that when I turn the power back on, the ARC breaker trips. If I reinstall the old breakers, there is no problem. What is causing the ARc breakers to trip?

Arc Faults work like GFI's in the sense that the hot and neutral need to draw equal current or they will trip.
A light may have a hot from one circuit and the neutral from another which would cause a problem.
If it is a Multi Circuit(2 hots sharing a Neutral, you will need a 2 pole 20 amp Arc Fault Breaker.
Unplug everything on that circuit and lights off and see if it trips.
You have the neutral of the Load on the Breaker and the Arc Faults Neutral on the Neutral Buss?

Arc faults are VERY sensitive devices and a bit of a pain for anything other than brand new wiring that you installed end-to-end. They can trip if there is a single loose connection to even one receptacle on that circuit.

First things, first - work on just ONE of those circuits at a time. Identify everything that is on it. Hopefully, the lighting and outlets don't share the one circuit. Then double-check all connections on that circuit to make sure they are really secure and properly secured with wire nuts / tape etc - with no exposed wire. Even just one loose connection will cause that arc fault to trip.

Good luck!

What is the model of your main panel and model Arc fault you are installing. Cutler hammer has a new arc fault that has 3 led's that will allow you to trouble shoot why it is tripping. It also eliminates the ground fault chip eliminating nuisance tripping.