All of a sudden my Mac users started complaining that they are unable to connect to or add a new Store to Citrix Receiver for Mac. Right after entering the NetScaler's URL and hitting Add, they receive an error stating "Could not detect the specified account" and "The server might be invalid or may be unavailable at this time. Make sure the URL is correct and check your network connection."
Nothing has been changed. Receiver for Mac was the latest version v12.1. No network issues, Safari works just well, navigating to the NetScaler URL, entering credentials, and launching a Citrix session. No certificate issues. Nothing, just as expected. I tried the script as mentioned here, but to no prevail.
Solution:
As all users came in from external networks through NetScaler, I had to disable EdgeSight Monitoring (HTML Injection) in NetScaler's System | Settings | Configure Advanced Features:
In my case I didn't have to disable AppFlow on my NetScaler's vServer as described by other users having the same issue. It already worked for me after disabling HTML Injection alone:
The same goes for having issues while connecting with Citrix Receiver for Android, receiving an error stating "An error has occurred while connecting. Check your server address and data connection". Have a look at Jason Samuel's blog article as well.
Further reading: