This reference includes information about the methods and usage of SharePoint Foundation Remote Procedure Call (RPC) protocol. This protocol can be used in Win32-based applications or in ASPX applications to make HTTP POST requests to the server. Methods in this protocol that do not modify the contents of the database can also be used in URL protocol to make HTTP GET requests.
Definition taken from http://msdn.microsoft.com/en-us/library/ms448359.aspx
You will find the OWSSVR.DLL in SharePoint 2010 Server Physical Path: C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\ISAPI and MOSS C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\12\ISAPI
Common mistakes Both SharePoint Site and SSO Site NOT running on the same application pool.Application pool identity user doesn’t have permission to access the certification.
Solution to this problem
Set the same identity pool to :
2. Be sure to grant rights to the certificate for the App Pool running the web service
Start -> Run -> MMCFile -> Add/Remove SnapinAdd the Certificates Snap InSelect Computer Account, then hit nextSelect Local Computer (the default), then click FinishOn the left panel from Console Root, navigate to Certificates (Local Computer) -> Personal -> CertificatesYou're certificate will most likely be here.Right click on your certificate -> All Tasks -> Manage Private KeysSet you're private key settings here.