Upgraded the box to 12.0-41.24 and now RADIUS authentication errors for the services there after are observed.
when configuring Authentication RADIUS server and pointing it to NetScaler local Load Balancer ip address we get error:

Server 'x.x.x.x' is reachable
​Either 'x.x.x.x' is not a valid Radius server'1812/udp' is not a valid Radius authentication port or Radius client is not configured properly on Radius server

Checked radius server config, SNIP of NetScaler was configured properly, password was matching, RADIUS service is up with a ping monitor bound.
In trace it is seen that NSIP reaching out to RADIUS LB VIP and nothing else.
LBVIP never forwards the request out

You can run a wireshark trace or nstcpdump.sh from shell to check connectivity between RADIUS server and NetScaler.

Command to run nstcpdump,

Go to Shell.
> nstcpdump.sh host <RADIUS IP>

Problem Cause