I was having troubles on OSX getting access to the KVM at work which is a Dell KVM 4322DS. The connection errors from Java about security settings were not resolved by whitelisting the site in the Java console. Turns out newer Java disables some SSL/TLS algorithms and settings that break the connectivity (rightfully so). Unfortunately not even a fully patched KVM fixes this, and people still need to access KVMs, so a workaround is needed.
After some Googling I came across some information that you need to edit the java.security file and change jdk.tls.algorithms.disabled. On OSX this file is at:
The setting originally looks like this:
jdk.tls.disabledAlgorithms=SSLv3, RC4, MD5withRSA, DH keySize < 768
I had to remove the "DH keySize < 768" to make this KVM work, but YMMV.