GUI cannot be accessed when using a server certificate with an RSA 1024 bit key
The GUI cannot be accessed when using an admin server certificate with an RSA 1024 bit key after upgrading to FortiOS 7.6.1, 7.4.8, or 7.2.11. An RSA key of at least 2048 bits is required. Certificates that are using an RSA key of less than 2048 bits are no longer supported.