If the CA-signed Certificate and CSR do not have the same information, the CSR cannot be imported. Check the following:
Are you trying to import the certificate to a device that does not have the same information?
Check the information of the CSR and then import the certificate to a device that has the same information.
Did you overwrite the CSR saved into the printer after sending the CSR to a certificate authority?
Obtain the CA-signed certificate again with the CSR.
You cannot import a CA-signed Certificate that is more than 5KB.
Enter the correct password. If you forget the password, you cannot import the certificate. Re-obtain the CA-signed Certificate.