Java (JCE) is refusing to process a certificate because it violates configured algorithm constraints. This is most likely a certificate using md5WithRSAEncryption that are still quite common.
The algorithm constraints are defined in
java.security file located somewhere in your JDK installation (e.g.
/etc/java-8-openjdk/security/java.security for OpenJDK8 on Ubuntu). Change the following lines
jdk.certpath.disabledAlgorithms=MD2, MD5, RSA keySize < 1024 jdk.tls.disabledAlgorithms=SSLv3, RC4, MD5withRSA, DH keySize < 768
jdk.certpath.disabledAlgorithms=MD2, RSA keySize < 1024 jdk.tls.disabledAlgorithms=SSLv3, RC4, DH keySize < 768