I'm playing with the NetApp Sim 8.2.1 and I'm getting 502 Proxy errors when trying to perform volume based configurations, I'm not sure what the hell is going on. For example trying to mount a volume to a root volume times out and that's when I get the Proxy 502 error. I've tried varous things such as removing java and system manager and reinstalling, removing the cluster and re-adding into the manager and nothing seems to be working. All the components I'm using are running in the virtualised envionment
vmware workstation v12
Server 2012R2 Standard Ed. for oncommand system manager / AD
Do you have any kind of proxy defined on your workstation? Even though it doesn't seem to be a problem for most requests, maybe some requests are built differently and would try to go to the proxy instead of directly to ONTAP.
In general I distrust 'server OSs' like Win2012 when trying to run what is normally a client-based tool like OC System Manager. Since you're running vmworkstation you're running windows something, have you tried SysMgr on your host OS to touch the vsims?