This might help:
Query-about-firmware-upgrade on Standalone APs
Updated: January 11, 2014 10:07 PM (about 1 month ago)
Do I have to follow a Upgrade path to perform firmware upgrade on Standalone APs
There is no upgrade path for performing firmware upgrades on Standalone APs. The Upgrade Path KB articles only apply to ZoneDirectors. You can upgrade the AP from any version to any more recent version in 1 step.
Article Number: 000001878