Here is the steps to reproduce the issue:

1. Create a normal user only belong to the jira-users group.
2. In the project permission setting, give the new user the permission "Administer Projects" without any project roles.
3. Login with the new user then go to the project administration page.
4. Try to remove users or group from a project role that has been granted the Administer Project permission from your permission scheme, and the error message will show up:

   You can not remove a user/group that will result in completely removing yourself from this role.
   

There are two possible workaround solutions:

1. Use a global JIRA admin user account to perform the operation.
2. Add your user account in the Administrators roles before the operation.