Auto-hiding of the taskbar is not supported on Windows 7 Tablet PCs where only touch or pen screen input is being utilized with no keyboard or mouse.
Windows 7 taskbar does not auto-hide on Tablet PC
If you enable the auto-hide feature, it can result in the taskbar being minimized beyond the boundary of the touch screen area. This becomes more apparent after configuring the Calibration option that can be found under Control Panel > Tablet PC Settings.
Calibration can further reduce the touch screen surface area around the border of the display to exclude the range needed to activate and restore the hidden taskbar.
To deactivate the auto-hiding of the taskbar, open Control Panel, and select Taskbar and Start Menu. Under the Taskbar tab, deselect the Auto-Hide the taskbar option.
The default setting for this option in Windows 7 is disabled, but if you have enabled it, you may want to disable it, recommends KB2495079!