ensure that high throughput is enabled in the 802.11a and 8011 g radio profiles. Also make sure that the high throughput is enabled in the ht ssid profile under the SSID profile.
rf dot11a-radio-profile "AP"
high-throughput-enable
rf dot11g-radio-profile "AP"
high-throughput-enable
wlan ht-ssid-profile "default"
high-throughput-enable