AR5001X+ (168c:0013) using wpasupplicant under 2.6.32 (Debian 2.6.32-3, though a diff shows the ath5k driver appears to be the same between this kernel and 2.6.32.13) cannot connect to a hidden SSID with WPA or WPA2 when using the 5.8 GHz band. It can connect just fine to a hidden SSID on the 2.4 GHz band via both WPA and WPA2 encryption. An earlier revision of ath5k, under Debian's 2.6.26 kernel, can connect to the hidden SSID on the 5.8 GHz band, but suffers from the noise floor calibration timeout issue.
Please attach the wpasupplicant.conf you are using.
Closing due to lack of response...