Set IIS Default Web Site\PowerShell authentication to allow basic.

I also activate Require SSL and Ignore client certificates.

Get your credentials:
PS>$Cred = Get-Credential

PS> $Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://server
/powershell/ -Credential $Cred -Authentication Basic –AllowRedirection

Attach to session:

PS>Import-PSSession $Session

Now you should be attached.

See sessions with PS>Get-PSSession, and remove them with PS>Remove-PSSession <ID>

Trubble shoot reference: http://technet.microsoft.com/en-us/library/dd351136.aspx