jw,
Make sure that there is not a refresh operation going on while you are changing data.
Look at the bottom of your browser window and check for the rising blue bar. If you see that at all, dont enter in any new data until it has refreshed the page.
I noticed that on the addresses, they have a dynamic list for the state counties that does not activate until you pick a state. Once you pick a state, the page refreshes to list the counties you can pick from. If you try to enter in data too quickly during this process, it will give you an error.
P.S. Why do they insist on having state county info for all these addresses? Its a royal pain the way they programmed it.