You may experience an issue where Attaché is only allowing maximum of 3 concurrent user logins at a time. If you experience this issue:
Go to the Help, About Attaché menu, and check the VIP number and User logins values.
If the VIP number displays 100170, then you are using a demo license VIP number. The Attaché demo license is limited to 3 concurrent users.
To resolve this issue you will need a new Attaché licence file. See: Request and install a new or updated Attaché Licence.