After renewing the certificate on NetScaler the external connections were no longer possible and the following errors are displayed in Citrix Reciever:
SSL error 84: "The field Key Usage is not valid"

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To resolve this issue request a new certificate where the field Key Usage contains the value Key Encipherment. This would be a requirement for a valid certificate.
Note: Data Encipherment is optional.

Problem Cause

The errors indicate that the new certificate received was not valid for SSL connections. The new certificate received was missing the value “Key Encipherment” under the field “Key Usage”.
Following is a screen shot of the old and new certificates to observe the differences. The old certificate is on the left side and the new one on the right.

CTX123519 - The Key Usage Field and the Client Certificate Authentication on an Access Gateway Enterprise Edition with Multiple Certificates