Symptoms

After navigating to Administration > User Repositories and choosing "Users and groups from JIRA or Crowd" to use JIRA or Crowd as a user repository, you get this error:

Failed to change the active user repository: At least one administrator 
required, but none were found. The following administrator groups were 
searched: [bamboo-admin]

Cause

The "bamboo-admin" group is missing from your JIRA or Crowd external repository.

Resolution

Bamboo must have at least one admin user, and at least one admin group ("bamboo-admin") in the external user repository. Create a bamboo-admin group in JIRA/Crowd and add users to the group.

Please note that the situation is different in case of an LDAP integration because after integrating Bamboo with an LDAP server, you will be able to use local and external user account. Related improvement request: BAM-11972 - Improve the error message of the Bamboo JIRA integration.