When I tried to install certificate to netscaler vpx, I got below error message:

Certificate with key size greater than RSA512 or DSA512 bits not supported

After investigate, I found that this problem is caused by Netscaler License. You need to install at least 3 licenses to Netscaler to support it’s functions

1) Netscaler Platform licence: this enables netscaler features, but more importantly, unlocks the higher grades of encryption. License issued against Host-ID (= mac addr)
2) Netscaler Gateway platform licences / ICA licenses: this licence gives you up "unlimited" basic mode (ie ICA-only) connections. License issued against Hostname
3) Universal licenses: paid for licenses (you get free ones with XD platinum / NS platinum) which allow use of smart-access mode (=vpn, clientless, or ICA with epa). License issued against Hostname.