Previous firmwares used a 1024 bit self-signed certificate, and updating the firmware does not update the self-signed certificate automatically.
Modifying the certificate will update the SonicWall to a new 2048 bit certificate and will resolve this issue.
Log into the SRA appliance and navigate to System | Certificates.
Select Configure for the Default Self-Signed certificate.
Modify the Common Name. (If the common name is correct simply change one character... then change it back after the reboot). You should consider using your domain name (EX: sslvpn.mydomain.com) instead of the IP address of the appliance.
Click Accept at the top of the page.
The SRA appliance will reboot after the change is applied to allow the changes to take effect.
How to Test:
Browse to the SRA management interface. Right click the lock in your browsers address bar to view the certificate. On the "Details" tab scroll down and find "Public key" this field should contain "RSA (2048 Bits)" after the steps. (Above)