If the IAP is part of a cluster, the username will be admin, and the password will be the serial number of any AP in the cluster. If the IAP is running a software version earlier than ArubaOS 8.5.0.0, admin will remain the default password.
ArubaInstant_Scorpio_8.10.0.14_90752
arubainstant_scorpio_8.10.0.zip
Aruba Instant-8.10.0.14 - release notes.