vCenter Server Appliance 6.0 : 503 Service Unavailable

503 Service Unavailable (Failed to connect to endpoint:
[N7Vmacore4Http16LocalServiceSpecE:0x7fc8bad2f810] _serverNamespace = /vsphere-client _isRedirect = false _port = 9090)

This is the error I'm constantly getting when trying to connect to the vCenter Server Web Client.

Details:

• I've installed the vCS Appliance 6.0 on an ESXi 6.0 host. It's running on top of it along other VMs.
• I can access the vCS appliance through an SSH client, but every attempt to access the web client ends with the error above.
• I've found that causes for this error are: the server being overloaded or under maintenance. However, I'm the only one to have access to this platform.

Any ideas?

I found the answer:

The problem was that I made a backup of the current vCenter appliance and stored it on the ESXi 6.0 without changing it's IP address. This created an access conflict. All I had to do is to change the IP address of the backup during its creation and the problem was solved