If you're school is doing a nightly sync, either with ClassLink, Clever or OneRoster, you have probably run into a situation where a user is in Enriching Students, but for some reason, was removed from the source data. When this happens, the user is "soft-deleted" in Enriching Students. The account is kept, but the user can no longer access Enriching Students.
Typically, this is exactly what a school wants. However, you may have created the user manually and forgot to select the "Ignore on Import" option. Or there could be a glitch in sending the data to Enriching Students. The user will be added back to the source data at some point, but in the meantime, you need to get the user reactivated.
If this happens to you, please go to Admin, and in the Manage Staff & Students section, look for Soft Deleted Users. This page will allow you to reactivate soft deleted users. Additionally, you'll have the option of setting the "Ignore on Import" option as well.