The AD FS Web Agent Authentication Service received a remote procedure call (RPC) from a user who is not in the IIS_IUSRS ...

The AD FS Web Agent Authentication Service received a remote procedure call (RPC) from a user who is not in the IIS_IUSRS group. 

This request will be denied. 

User Action 
If this error results in failed AD FS authentications, ensure that the failing Internet Information Services (IIS) application pool's identity is a member of the IIS_IUSRS group.