This information applies to version(s): 1, 2, 3, 4, 5, 6
There are multiple reasons that could cause this issue. Please open a ticket with customer support and include the exact error message you're receiving.
To get help from DxO Support Team directly from this page, please click on this link.
Note: screenshots are extremely helpful and allow us to see what's on your screen. Please attach them in JPEG format to your ticket here.