ASA5505 to cascade two switches.

Hello...

I have lab with ASA 5505 as a router, port 4 and port 6 are configure at the same internal VLAN subnet, port 6 connect to Switch1 (2960), port 4 connects to Switch2 (3960), any hosts connects to Switch1 and Switch2 can connect to each other and to the internet without problem.

Now, when I reconnect Switch2 to port 23 of Switch1, hosts in Switch2 lost the connection to the rest of the world except those hosts in the same switch (switch2), that they can communicate each other.

What needs to be changed when cascade a switch to another in this configurations?

Thanks, Yvette.