Active Directory Federation Services (ADFS) is used by Microsoft Dynamics CRM for an Internet Facing Deployment (IFD). Relying Parties are used to allow users to be authenticated when trying to access Microsoft Dynamics CRM.
The default settings require users to re-authenticate every hour if there is no activity. This can quickly become annoying if users have to sign in to CRM several times a day. ADFS gives administrators the ability to increase the timeout and reduce the need for users to repeatedly sign in through out the day.
Your session has expired
To change the timeout value, you will need to update the TokenLifetime value. This is achieved using PowerShell. Before you open PowerShell, you will need to find the name of each Relying Party.
ADFS Relying Party List
get-ADFSRelyingPartyTrust -Name “CRM – Local”
Set-ADFSRelyingPartyTrust -Targetname “CRM – Local” -TokenLifetime 480
Source: QGate Knowledgebase