You will get this error
->
Http Error - 500
{"message":"Unexpected error:There was a problem while sending query to service https://<hostname>:7116/dp-gui/grePlugin/GetMountProxies.jsp. Check that this agent is accessible."}
<-
when HP OneView for VMware vCenter is also installed. There is a CR (QCCR2A65688) already raised for this issue and currently pending decision by R&D. The issue is also present in DP9.05.
The obvious workaround is to uninstall HP OneView but this is not a viable option for many customers.
I found another workaround which worked for me.
When the "VMware vSphere Web Client" service is restarted with no plug-in executed yet. At this point DP vmware adv GRE will still work. Once customer click on "HP Management" tab, and OneView plug-in is executed, after this point DP vmware adv GRE will fail with the above error.
So when DP vmware adv GRE report the error, the workaround is to restart the "VMware vSphere Web Client" service and make sure not to execute the OneView plug-in by clicking "HP Management" tab, until they have finished with using DP vmware adv GRE.
Hopefully this workaround would be more acceptable, until there is a permanent fix from R&D.