I’ve been having problems with my Airport Express hanging when I’m putting lots of traffic through it. This usually results in me resetting it to get it working again.
After a bit of research on Apple’s Disscussion pages, I came across the following tip:
Open Airport Admin Utility, select the AE and click configure. From the new window click the Network tab. Under AirPort client computers, select "Share a single IP address". From the drop down list choose "Use 172.16.1.1 addressing" (ANYTHING apart from the 10.0.1.1 option, I think this is the problem?). Next click the update button at the bottom right of the window.
If you’re having problems with your Airport Express dropping the connection, hanging, stalling, etc…you might want to try making this minor adjustment. It seems to have solved the issue for me.