Well there are a few things that could be causing it.
The first thing I would suggest you do is restart your modem/router. Although, as you say, the other device works fine with it, that is no guarantee that any other device will. Tablets can be quite picky.
Second thing to do, after or while you restart the modem/router, also restart your tablet. However, make sure the tablet does not load first. It needs to finish restarting after the modem/router.
Third, if necessary, remove the data/info for your connection on the tablet and then re-add it.
Fourth, make sure you check, and if necessary adjust, the WiFi sleep policy on the tablet. It can often cause this.
To check to see if this is the issue...
1. On the home screen of your tablet go to "Menu" then "Applications".
2. Next go to "Settings" and finally "WiFi Settings".
3. On this screen tap the "Menu" button and then choose "Advanced".
4. Now you want to choose "WiFi Sleep Policy".
It should show you options, including one for when the screen turns off. If it is set to do this, then the WiFi will automatically be disabled, and go into "Standby Mode", as soon as the screen goes dark. Also there will be options like "Never When Plugged In", so that the WiFi will go down if you plug the tablet in. Go through each of the choices your device gives you in here, and make sure it is not set to turn it off for such reasons. You also have the option to set it to "Never" disconnect from the WiFi.
Lastly, I would make sure that there are no apps that were recently installed, or updated, that could be causing it to disconnect. Either through just messing with the connection (yes some are just made to annoy) or by trying to do things through the WiFi and it keeps kicking it out. So I would check the device.
One of these should fix the problem.
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