Double check what the IP addresses are for the devices (and the subnet mask) to verify they are on the same subnet. How does your smartphone know what the IP address of the tablet is you want to talk to - DHCP hands out the addresses, but you don't have any DNS at that point, so it does not know how to convert from the tablet name to an IP address (or are you using the IP addresses for your communication - that would take out the DNS issue). The error message you posted has the look and feel of the two devices being on different subnets or something.
mikey