ZyXEL Communications P-334WT Support Notes page 191

So, the Key 3 of station has to equal to the Key 3 of access point.
Though access point use Key 3 as default key, but the station can use the other Key as its default key to encrypt wireless data
transmission.
Access Point (encrypt data by Key 3) --------> Station (decrypt data by Key 3)
Access Point (decrypt data by Key 2) <-------- Station (encrypt data by Key 2)
In this case, access point transmits data to station which encrypt data by Key 3 of access point. The station will decrypt the data
by its Key 3.
At the same time, when the station transmits data to access point which encrypt data by Key 2.
The access point will decrypt the data by its Key 2.
Setting up the Access Point with Web configurator
Key settings
Select one WEP key as default key to encrypt wireless data transmission.
Setting up the Station
1. Double click on the utility icon in your windows task bar or right click the utility icon then select 'Show Config Utility'.