I'm new here, but do you use an interface that is supported by Pro Tools? If not, it could be the INTERFACE/SOUNDCARD that is causing the error in ProTools. As you said, the keyboard itself works fine.
Interface Compatibility with ProTools:
Fast Track (inlcuded with Avid Recording Studio)
USB Micro (included with Avid KeyStudio)
Producer USB (included with Avid Vocal Studio)
MobilePre (includes Pro Tools SE software)
Fast Track Pro
Fast Track Ultra
Fast Track Ultra 8R
Other interfaces won't work, apparently.
And a google search brought me here:
http://www.avid.com/US/products/Pro-Tools-Software/
You can click the 'Free Trail' button on the right to fill in your details and download (I guess).