This message is displayed when:
- Your target site has one xxxx user (xxxx being the username)
- The backup being restored also has one xxxx user.
- After various comparisons, Moodle has detected that the xxxx user in 1. and the xxxx user in 2 are not the same user.
If 1, 2 and 3 error message comes, restore stops before performing any action as far as restoring that user will end associating "things" (create activities, posts, attempts....) to the xxxx user in the target site, when those "things" weren't performed by the user at all.
Usually the xxxx user in the messages is the "admin" user.
There are two possible solutions to make both xxxx users in 1 and 2 to match (and avoid the conflict):
a) Modify the backup's users.xml file and make the email or firstaccess fields match with the ones in target site.
b) Modify the target site and set the user email or firstaccess fields to match with the ones in backup's user.xml file.
Method a) is recommended so the restore process will match both xxxx users and every "thing" in the backup file belonging to xxxx will be associated to the already existing xxxx user in the target site.