Thats the minimum release supported to deoploy it as remote AP
If you read the release notes of the 6.2 you will see this
RAP-3WN and RAP-3WNP Remote Access Points
This release of ArubaOS introduces support for RAP-3WN and RAP-3WNP access points (APs). The Aruba
RAP-3WN and RAP-3WNP are single-radio, single-band wireless APs that support the IEEE 802.11n
standard for high-performance WLAN.
Do you have Rap3 that you need to deploy as Remote AP?
Remember to read the release note and the readme file before upgrading to this version... its really important!