The OS of MAC needs to be checked first. The latest MAC OS X 10.12.5 is not officially supported with OBM v6.
Apart from that, OBM fails to connect via https with the Java 1.8.0_71 or above installed on the MAC machine since the MD5 is disabled.
In this case, try editing the JVM's "java.security" (/library/Java/JavaVirtualMachines/jdk1.8.0_71.jdk/Contents/Home/jre/lib/security/java.security) to enable MD5.
Change the following settings in "java.security":
jdk.certpath.disabledAlgorithms=MD2, MD5, RSA keySize< 1024
jdk.certpath.disabledAlgorithms=MD2, RSA keySize< 1024
jdk.tls.disabledAlgorithms=SSLv3, RC4, MD5withRSA, DH keySize< 768
jdk.tls.disabledAlgorithms=SSLv3, RC4, DH keySize< 768
Once done, please reboot the Mac machine and see if you can login OBM on the problematic Mac machine.
After that right click the security folder and allow all READ WRITE access to java. Security as well, since they are read only to start.