Cannot join this farm because it contains server assigned to the single server farm role.

I was trying to connect central administration,i was getting error as displayed in snapshot,so i disconnected from SharePoint configuration wizard.

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Now i'm  trying to run SharePoint configuration wizard again to connect existing server farm,it gives me below error

"cannot join this farm because it contains server assigned to the single server farm role.To join an additional server to this farm first disconnect server from the farm and then try again"

 Please help..

syn_snehal