[chef] Error in chef-server web ui

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Hi

I installed chef-server on a server machine, but on accessing the Web UI

I'm getting the following errors

1. Users -> "ERROR: undefined method 'name='for nil:NilClass''"
2. Clients -> "Could not list clients: 403 "Forbidden""
3. Nodes (When assign roles to the node) -> Exception raised updating node, 
403
"Forbidden": 403 "Forbidden"

Thank you.