From hnowledge base :
You may encounter this error when attempting to launch Avid Xpress Pro HD.
Go to C:\Program Files\Avid\Avid Xpress Pro HD and look for digitalio.dll If it’s there, delete it.
Also look for and delete CoreUtils.dll, CoreServices.dll, CoreThreads.dll and LavaFlow.dll – but ONLY in the Avid Xpress Pro HD folder.
Once you’ve done this, restart your computer and launch Xpress Pro HD.
If it still does not launch, save copies of your Avid Projects and Avid Attic folders to your desktop (if you have projects from a previous version that you wish to save), and go to Control Panel > Add or Remove Programs. Remove Avid Xpress Pro HD and Avid DIO Runtime. Then go to C:\Program Files\Avid and delete the Avid Xpress Pro HD folder, and finally delete the Avid folder from C:\Program Files\Common Files. Restart your computer, and reinstall Avid Xpress Pro HD.