Using multi-org feature I am unable to create a sandbox account, why is that?

Using multi-org feature I am unable to create a sandbox account, why is that?

The possible reasons for not been able to create Sandbox account could be:
  1. You may not have create permission in the production CRM org.
  2. You are already part of 10 sandbox orgs.
  3. You are already super admin in 5 sandbox orgs.