Error "Your account cannot be added using this server address. Make sure you entered it correctly. You may need to enter your email address instead." when trying to logon Gateway URL via Citrix Workspace. 

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Create and apply Advanced Authentication Policy in NetScaler

1. Go Security>>AAA-Application Traffic>>Policies>>Authentication>>Advanced Policies>>Policy
2. Click Add to create new Advanced Authentication Policy

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Problem Cause

Classic Policy Expression has been deprecated, which is replaced with Advanced Policy Expression now. NetScaler NOT support to apply both Classic Policy and Advanced Policy together.
All applied Policies in NetScaler, like Authentication Policy, Session Policy, Rewrite, Responder Policy. etc, their policy expression MUST write in Advanced Policy Expression format.

In NetScaler Gateway, the most common symptom we met is: Authentication Policy is configured with Classic Policy Expression, while Session Policy is with Advanced Policy Expression. This will result the Authentication Policy unable to be evaluated. User access finally blocked with authentication failure.

Click here for more info regarding to Classic/Advanced Policy Expression in NetScaler

If you're interested in real-time policy evaluation or hit in NetScaler, you may run below command in Shell CLI to check

#nsconmsg -d current -g _hits

Press Control + c to exit command.