Unable to load CA private key when creating the intermediate pair

Following the tutorial at LINK to create the root pair and intermediate pair.

Creating the root pair works fine, but when I try to create the intermediate pair using:

openssl ca -config openssl.cnf -extensions v3_intermediate_ca -days 3650 -notext -md sha256 -in intermediate/csr/intermediate.csr.pem -out intermediate/certs/intermediate.cert.pem

I get the following error:

Using Configuration from openssl.cnf
Can't open /root/ca/private/ca.key.pem for reading, No such file or directory
140382210524824:error:02001002:system library:fopen:No such file or directory:crypto/bios/bss_file.c:398:fopen('/root/ca/private/ca.key.pem','r')
140382210524824:error:20074002:BIO routines:BIO_new_file:no such file:crypto/bios/bss_file.c:76:
unable to load CA private key

The ca.key.pem file was encrypted using:

chmod 400 private/ca.key.pem

And I verified that I can see the CA's private key file using:

ls /root/ca/private/ca.key.pem

What is wrong?

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