when I installed the vsphere web client use vcenter server iso , encounted an error that the vcenter server signon administrato use name and password was invalid

Vcenter server is 5.1 version and this server is a workgroup member.

this is my administrator :

When I used vcenter server ISO ,and installed vsphere web client pulg-in, it prompted :

I Used many ways but failed.

usernme:admin@System-Domain  ,

so ,I don't know how to resolve it ,and I only know this administrator password .

I'm not sure vCenter Single sign on have other admin,please help .

and have other question: how to install and configure the vsphere data protection via the vsphere client 5.1 , is not vsphere web client.