We have been sharing the ACT 10 database between three users for about a month with no issues. Today, we accidentally unplugged our Netgear router while all users were connected to the database. After the router was plugged back in, when non-host users are trying to access the database, we get an error that says the database is not shared. I have checked the database within ACT to confirm it is set to "Share Database", and it is.
We got it working again. We had the host or something like that have a direct route to each computer. Since we are DHCP, when the router rebooted it assigned the machine with the database a different IP address. When we removed the direct link, we were good to go!