Cannot use previous account key

[acastiello]

I have an account key that I use with other ACME clients. I can´t use it with PJAC
java -jar acme_client.jar --command order-certificate -a "my_old_account_key.pem" -w . -c csr.pem --well-known-dir "D:\Internet\WEB\mydomain.com.well-known\acme-challenge" --one-dir-for-well-known --server-url https://acme-staging-v02.api.letsencrypt.org/directory
but I get
Exception in thread "main" java.lang.ClassCastException: org.bouncycastle.asn1.pkcs.PrivateKeyInfo cannot be cast to org.bouncycastle.openssl.PEMKeyPair
Does PJAC requires a new account?