On-screen keyboard not working when USB barcode scanner is connected Problem

When you connect a USB barcode scanner, the on-screen keyboard of your Android Tablet may stop working. To resolve this problem, take the following steps:

Open the Applications tab and tap Settings.
Tap Language & Input, and next Current input method.
Disable the Use Physical Keyboard option.

from : http://acer--uk.custhelp.com/app/answers/detail/a_id/12300/~/on-screen-keyboard-not-working-when-usb-barcode-scanner-is-connected