CMS user IDs cannot contain diacritical marks, accented characters, special characters, punctuation, or spaces. For example, á, ñ, ç, |, ©, and _. Older CMS releases might include IDs with unsupported characters. Before starting the upgrade, update these user IDs to use only alphanumeric characters. Ensure each user ID is between 3 and 8 characters long. For example, change Dave_15 to Dave15.