When you attempt to open a virtual machine console from the vSphere Web Client, the console does not connect. The following error message appears:

Why did not connect?

A. Port 443 is in use.

B. Port 9443 is in use.

C. Port 8443 is in use.

D. Port 22443 is in use.

Explanation:

Another program or process is using port 9443, the default port used by the HTML5 virtual machine console.

Reference:

https://docs.vmware.com/en/VMware-vSphere/6.5/com.vmware.vsphere.troubleshooting.doc/GUID-8536C14F-4D4F-4674-846E-08BE321B7A11.html