A Load Balancing Virtual Server that is protected by a Form Based Authentication AAA vServer.
Users have started complaining that after authentication to the AAA vServer, they get an error message "Target URL is not found", randomly.
The users who get affected by this, can refresh the page and it will work.
This happens to all users.

The ns.log files at the time show the below error:
"AAA Client Handler: Found extended error code 262157, ReqType 16388 request /cgi/login, cookie hdr "

Users need to access the Load Balancing Virtual Server first, which then inserts the cookie to the browser. This then allows the ADC to know where to redirect the authenticated users. 

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Problem Cause

Found that the affected users where connecting directly to the AAA login page, instead of to the Load Balancing Virtual Server first, which means the NSC_TASS cookie is not getting inserted into the clients; browsers which causes the issue

https://support.citrix.com/article/CTX208789