Thought it might be good to post the bug and the way to solve it here, because it took me much time to find something on google.
Everytime I started something made with the RM VX ACE the character just walked to left until he reached the end of the map.
For the people who haven't any gamepad plugged in... I found this:
http://www.rpgmakervx.net/index.php?showtopic=797
That is not a bug in RM, it's a problem in the Windows API that can't be fixed...
In early windows versions (before tablets, USB or other input devices were affordable to most users) Microsoft created an API for input that was designed mostly for single devices - the developers didn't think that anyone might mix graphical tablets (which were 1000$ up for the most simple ones) and game controllers (of which only a few models existed at all) would be used on a PC much - and not in combination at all.
As a result there were many problems when several programs and device drivers tried to access that at the same time, and as a result, newer Windows versions got a different API for that. The new API has a general driver inbuild and does not need a device driver at all, Windows will automatically detect all special functions of graphics tablets or game controllers.
The device drivers for special input devices are only neccessary if your windows is so old (Win9x, ME, 2K) that it cannot automatically detect the tablets or game controllers - and in that case, those drivers force windows to deactivate the more modern API and switch to the ancient API which still remains bug-ridden as soon as you get a multiple access on that API.
That is also the reason why it doesn't matter if the tablet or gamepad is connected: the driver forces Windows to use the old API as soon as it is installed, even without having the device connected.
And that is why the easiest way to solve this in more modern Windows versions (and that is anything from XP up if I remember correctly) is to remove the completely unneccessary driver that forces Windows into the old API for input devices, and allow the newer (and bug-free) API with the build-in-drivers handle everything.
EDIT:
By the way, google is a very bad search engine for such specific topics - if you had searched directly on this forum, you would have found half a dozen posts about the same problem and how to solve it.