1-When you see this message in your tablet, or any computer conected to the server using a WIFI signal, it means they are probably not in the same network.
To check this you will have to check both the server and the computer/tablet conected to it.
2-Checking a computer’s IP address:
2.1-Windows 7: Click on the Start button 
, and then type down in the search button “CMD”. Click on the “CMD.exe” option.
2.2-Windows 8: Open the All programs page, and find the search field in the upper right corner. Type down in the search button “CMD”. Click on the “CMD.exe” option.
2.3-Windows 8.1: Right-click in the Start button and select the option “Command Prompt (Administrator)”.
2.4-In all cases, you will see the screen below:
2.5-Type down the command “IPCONFIG /ALL” and press ENTER in the keyboard.
2.6-The IP in this case is 192.168.1.11
3-Checking a tablet’s IP address:
3.1-Apple iPad:
Go to setting on your iPad
Select ” WiFi ” from the sidebar.
Tap on the arrow next to the network name.
Your IP address will be displayed to the right of “IP address”
Select “Settings”.
Select “Wireless & networks”.
Select “Select the network you are currently connected to under “Wi-Fi networks.
The IP address should be displayed with other network information.
4-For the 2 devices to be in the same network, the IP addressess must be equal until the last number.
Using the example above, all IPs, in all computers and tablets must be 192.168.1.XX, with the 2 XX being the only part that can be different.
If any other part is different, it means they are not in the same network, and the system will not work in other devices besides the server.
5-Another possibility is the Webservice is wrong in tablets. Open the Webgerencial App and click in the Webservice option. It must be the local address when in the same network, and the internet address when in a different network.
You can also try to open the webservice using the tablet’s browser to see if it works.
6-Even other possibility is that the server is not turned on (the computer itself) or the Webgerencial program is not functioning/was started correctly.